Error with Microsoft Project subprojects stored in SharePoint

Anonymous
2026-08-31T12:32:22.6+00:00

I'm using Microsoft Project Professional (desktop app) with a master project file and multiple linked subproject files, all stored within the same SharePoint document library.

I'm encountering several recurring issues:

  1. File locking / read-only access
  • Other team members need to be able to open and view the master project and subprojects.
  • However, if anyone has a project open, even in what appears to be read-only mode, I can no longer edit or save changes.
  1. Broken subproject links
  • The master project and subprojects can be fully linked and saved correctly one day.
  • When reopening the master file later, some or all subproject links are broken and need to be reinserted/relinked.
  • The files remain in the same SharePoint location and have not been moved or deleted.
  1. Password-protected reservations disappearing
  • We use password-to-modify protections on the project files.
  • These settings occasionally disappear without being intentionally removed.

All files are .MPP files stored in SharePoint Online and opened using the Microsoft Project desktop application.

At this point I'm trying to determine whether these are known limitations of using Master Projects/Subprojects from SharePoint rather than a configuration issue on the our end. Has anyone experienced similar issues and found a reliable solution or workaround? Any advice is much appreciated.

Microsoft 365 and Office | Project | Other | Other
Microsoft 365 and Office | Project | Other | Other

Microsoft project management software used to plan, manage, and communicate a project schedule and other information among workgroup members, project managers, and other stakeholders.

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Answer accepted by question author
Kristen Tran 1,520 Reputation points Independent Advisor
2026-08-31T13:00:08.52+00:00

Good day,

Based on the information available in Microsoft's documentation, the behavior you are experiencing appears to be related to the way Master Projects and linked Subprojects function when stored as separate .MPP files in SharePoint Online, rather than a known product issue affecting all environments. Linked subprojects remain independent files, and updates made from the master project can be written back to the source subproject files. As a result, this setup is not designed to support simultaneous editing in the same way as Office applications such as Word or Excel.

This may help explain the file locking and read-only behavior you are seeing. When a master project is opened, Project may need access to the linked subproject files, and SharePoint, OneDrive synchronization, or file-locking mechanisms can sometimes prevent other users from making or saving changes at the same time.

Regarding the subproject links, these links depend on references to external project files. Although the files remain in the same SharePoint library, differences in how users access them, such as through SharePoint, OneDrive-synced folders, cached Office locations, or other paths, can occasionally affect how those links are resolved when the master project is reopened.

For more information:

For the password-to-modify settings, I was unable to find documentation indicating that SharePoint intentionally removes these settings or that this is a documented limitation. To help investigate further, I recommend reviewing the SharePoint Version History to identify when the protection was removed and whether a previous file version may have replaced the protected copy.

As a best practice, you may want to consider the following:

  • Assign a single designated editor for the master project and linked subprojects.
  • Use SharePoint check-out/check-in features to help reduce edit conflicts.
  • Ensure all users open the files using the same access method.
  • Provide PDF exports or read-only copies for users who only need to review project information.
  • Keep SharePoint versioning enabled to assist with tracking and recovering unexpected changes.

If maintaining stable links between multiple projects is critical to your business process and multiple users need to work with the schedule concurrently, you may also want to evaluate a more centralized project management solution instead of relying on linked .MPP files stored in a SharePoint document library.

For reference:

I hope this helps clarify the behavior you're seeing. Please let me know if you have any additional questions.

Kind regards.

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