Introduction

The OnePlan Microsoft Project connector lets project managers keep building detailed schedules in Microsoft Project while OnePlan provides portfolio, resource, and financial visibility. The two tools were built for different purposes and use different scheduling and calculation logic, so some information may look different after you publish or update, or may not transfer at all.

While a plan is connected, Microsoft Project is the source of truth for the schedule. This article lists the known gaps and differences so you can plan around them, and understand why your data may look slightly different than you expected.

How to Read This Article

• Gap: something one tool supports (or expects) that the other does not. You may need a workaround.
• Difference: both tools support the feature, but they calculate or display it differently by design. Nothing is broken, but results may not match exactly.

Each entry is tagged with an Area (Scheduling, Calendars, Resources, Costs, or Fields) and follows the same format:

• What you may see: the symptom.
• Why it happens: a short explanation.
• What to do: a recommendation or workaround.

Quick Reference

Known Gaps

Negative lag that moves a task before the Plan Start Date

Gap  |  Area: Scheduling

What you may see: After publishing, the plan's Work Plan in OnePlan freezes or stops working. In the browser's developer tools, an error appears in the console. In Microsoft Project, the schedule itself looks normal.

Why it happens: : In Microsoft Project, a task can have a negative lag (lead) on a predecessor link. If the lag is large enough, the task is scheduled to start before the first tasks start date. Microsoft Project allows this. OnePlan does not support this, so the Work Plan cannot load the schedule.

What to do: Before publishing, check that no task starts before the .mpp files first task start date. If one does, reduce the negative lag on that link, or move the project start date earlier in Microsoft Project, so every task starts on or after it. Then Publish again.

Enterprise (Project Online) resources cannot be mapped

Gap  |  Area: Resources

What you may see: A warning during Map Resources stating that Enterprise Resources can't be mapped and only local resources are mappable.

Why it happens: The connector can only write OnePlan information into local resources. This commonly occurs when a plan was downloaded from Project Online using Save As > Save Locally, which leaves User Logon Account information in the file.

What to do: Clear the User Logon Account values from the Resource Sheet, or clear the Microsoft Project cache, then connect and publish again. 

Tasks cannot be added in OnePlan while a plan is connected

Gap  |  Area: Scheduling

What you may see: You cannot add tasks to the Work Plan Schedule in OnePlan, including External Tasks. Link and Unlink, Plan Start Date, and Insert Template are also unavailable.

Why it happens: The Microsoft Project file is the source of truth for the schedule, so schedule structure can only be changed there.

What to do: Add or restructure tasks in Microsoft Project, then Publish. If you need to build the schedule in OnePlan instead, disconnect the plan first (see "Disconnecting a plan can change task dates").

Cost resources do not receive cost values from OnePlan

Gap  |  Area: Costs

What you may see: Cost-type resources in Microsoft Project have no cost populated from OnePlan.

Why it happens: Cost resources do not use Cost Rate Tables in Microsoft Project, and OnePlan does not push Cost or Cost Table values to them.

What to do: Enter Cost resource values manually in Microsoft Project, through the Task Information form.

Cost Tables sync to Option A only, with a row limit

Gap  |  Area: Costs

What you may see: OnePlan Cost Table data appears only in Option A (Default) of the resource's Cost Rate Table, and long tables are cut off. Existing Option A data is overwritten. Options B through E are untouched. A warning appears on Publish if a task uses a table other than Option A.

Why it happens: OnePlan has a single Cost Table with no row limit. Microsoft Project has five Cost Rate Table options with up to 25 rows for each Cost Table option.

What to do: Use Option A (Default) for tasks that rely on synchronized OnePlan Cost Tables. Keep OnePlan Cost Tables under the Microsoft Project row limit; when a table is longer, only the first 24 rows from the OnePlan Cost Table are imported into Microsoft Project and the default first row keeps a Std. Rate of 0. Cost Table Synch is off by default and must be enabled per file. 

Resource calendars are not synced back to OnePlan

Gap  |  Area: Calendars

What you may see: A calendar assigned to a resource in Microsoft Project does not appear on that resource in OnePlan, and a mismatch between the two does not cause any change.

Why it happens: Calendar sync only affects task calendars in the OnePlan Work Plan. OnePlan calendars are imported into the project file, and task calendars set in Microsoft Project are applied in OnePlan. Resource calendars in the OnePlan Resource Center are not affected.

What to do: Maintain resource calendars in the OnePlan Resource Center. Use imported OnePlan calendars for tasks.

Progress: % Complete or Actual Hours, not both

Gap  |  Area: Fields

What you may see: You cannot map both % Complete and Actual Hours at the same time.

Why it happens: Microsoft Project supports mapping one or the other for progress.

What to do: The default is % Done (OnePlan) to % Complete (Microsoft Project). To also see Timesheet Hours, map them to a custom field in Microsoft Project. Alternatively, remove the % Complete mapping and map Timesheet Hours to Actual Hours to track by time instead of percentage.

Known Differences

As Late As Possible constraint on parent tasks

Difference  |  Area: Scheduling

What you may see: A parent (summary) task can have the As Late As Possible constraint in OnePlan, but not in Microsoft Project.

Why it happens: Microsoft Project only allows this constraint on child tasks. Constraint Types and Dates flow from Microsoft Project to OnePlan on Publish.

What to do: Apply As Late As Possible to child tasks only. All other constraint types behave the same in both tools.

Scheduling Mode and Task Mode are fixed while connected

Difference  |  Area: Scheduling

What you may see: Scheduling Mode is always Normal and Task Mode is always Manually Scheduled in OnePlan, regardless of the plan's Default Task Type.

Why it happens: Microsoft Project's scheduling engine calculates the dates, so OnePlan's scheduling engine does not.

What to do: Make date and scheduling changes in Microsoft Project and Publish.

Disconnecting a plan can change task dates

Difference  |  Area: Scheduling

What you may see: After disconnecting, Scheduling Mode changes to the plan's Default Task Type, and Start and Due dates may change. Fields that were read-only become editable.

Why it happens: OnePlan's scheduling engine takes over from Microsoft Project's. The confirmation message warns that tasks will be set to Automatic and changed to your default scheduling mode.

What to do: Review dates after disconnecting. We do not recommend disconnecting only to reconnect later; keep a plan either connected or disconnected. The connection details stay stored in the Microsoft Project file and only matter if you later connect it to a different plan or group.

Back-to-back availability ranges are shortened on import

Difference  |  Area: Calendars

What you may see: A OnePlan calendar with two availability ranges and no gap between them (for example, 8:00 AM to 12:00 PM and 12:00 PM to 5:00 PM) imports as 8:00 AM to 12:00 PM and 4:59 PM to 5:00 PM. No error appears.

Why it happens: Microsoft Project requires a gap between the two time ranges.

What to do: Leave a gap between ranges in the OnePlan calendars, for example 8:00 AM to 12:00 PM and 12:30 PM to 5:00 PM.

One holiday per day, and unique holiday names

Difference  |  Area: Calendars

What you may see: Calendar sync errors: either "Exception day error ... conflicts with a pre-existing exception on this calendar," or "An item with the same key has already been added."

Why it happens: Microsoft Project allows only one holiday per calendar day, and every holiday name on a calendar must be unique, even across different years.

What to do: Delete or move holidays that share a day, and include the year in recurring holiday names (for example, Labor Day 2026). If you do not wish to sync calendars, turn off the calendar sync in the OnePlan Extension settings.

Cost Table dates work differently in each tool

Difference  |  Area: Costs

What you may see: Cost Table rows in OnePlan have start and end dates, while Microsoft Project shows only an Effective Date, and a rate stays active until a new row replaces it.

Why it happens: OnePlan requires a Start and End Date on every row, and rejects overlapping rows. It allows gaps, but the cost during a gap is assumed to be 0. Microsoft Project does not allow gaps or overlaps.

What to do: Avoid gaps between rows so resources scheduled in those periods do not produce unexpected cost values.

Shared With members are added to Map Resources automatically

Difference  |  Area: Resources

What you may see: When you open Map Resources, people on the OnePlan plan's Shared With list are added as new resources, or replace an existing resource with exactly the same name.

Why it happens: Shared With members are mapped automatically at any permission level, including No Access.

What to do: Review the Shared With list before opening Map Resources, and check the mapping before you Publish. Mapped resources also store their OnePlan resource Id in the Text30 field.

Mapped fields are read-only in the OnePlan Work Plan

Difference  |  Area: Fields

What you may see: Any field with an active field mapping cannot be edited in the Work Plan. Bi-directional fields can only be updated by the assigned user in My Work.

Why it happens: This keeps data consistent between the tools. Bi-directional updates are sent as proposed changes that the Project Manager reviews in Microsoft Project, then publishes back. The field must be configured as a Status Field.

What to do: Update mapped fields in Microsoft Project, or configure bi-directional fields as Status Fields for My Work. Field mappings apply to the entire OnePlan group, not just one plan.

Tips to Avoid Surprises

• Keep the Microsoft Project connector on the latest version; only the latest is supported.
• Start with a plan that has no Work Plan Schedule items. Connecting deletes existing items (tasks with logged timesheet hours are kept and listed in a message).
• Remember that a plan does not show as connected in OnePlan until the first Publish.
• Give each calendar a short name, a gap between availability ranges, and unique holiday names.
• Decide up front whether you will use Cost fields or Cost Tables, and enable Cost Table Synch before mapping resources.