IMPORTANT UPDATE: Microsoft Project Online Retirement scheduled for September 30, 2026. From this date Project Online will no longer be accessible, however we can help you transition to Planner Premium and the Wellingtone Accelerator+ or to Project Server Subscription Edition.
Microsoft Project Online gives users the flexibility to edit schedules either directly in the browser (for simple edits) or via Project Professional, which provides full scheduling functionality. However, there are occasional issues when attempting to edit schedules in the browser or when trying to connect through Project Professional.
This guide walks through the common causes of these issues and provides practical, step-by-step resolutions to help you get back on track.
This guidance applies to Project Professional 2016 and later, including Microsoft 365-based versions. Some steps may differ slightly for older installations.
Issue: Unable to edit a schedule in Project Online from the browser
If you’re receiving errors when attempting to open or edit a schedule in the browser, a common culprit is the presence of blank lines in the schedule. These can exist either between tasks or after the final task in the list, often as a result of copy-pasting from Excel or other project plans.
How to fix it
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Open the project in Project Professional (if you don’t have it installed, ask an administrator to assist).
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Carefully review the task list and remove any empty rows between tasks.
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Scroll past the last visible task – blank rows at the end are frequently overlooked but can still cause errors.
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Once cleaned, Save, then Publish, and finally Check-in the project.
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Return to the browser and attempt to open the schedule again. You should now be able to edit without errors.
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How to prevent future browser edit issues
To avoid running into this problem again:
- Avoid copy-pasting tasks directly from Excel or other sources without reviewing for formatting issues
- Train project managers and team members to check for and remove stray blank rows
- Always scan the end of the schedule before publishing, especially when making bulk edits
A cleaner schedule helps ensure better compatibility with both browser and desktop editing.
Browser-specific behaviour
While Project Online supports all major browsers, cached data or browser-specific quirks can occasionally interfere with editing.
If errors persist even after cleaning the schedule:
- Clear your browser cache and cookies
- Try accessing the project in an alternate browser (e.g., Microsoft Edge, Chrome)
This can help rule out local browser-based conflicts.
Issue: credential prompts or failure to connect with Project Professional
You may also run into trouble when trying to open a project in Project Professional via Project Web App (PWA). Typical symptoms include:
- Failure to connect to PWA from Project Professional
- Repeated prompts to enter Office 365 credentials
- The “Connect to Project” error message
In many cases, these issues are related to cached or incorrect credentials stored on the local machine.
How to fix it
- First, confirm you have the required permissions to both open and edit the project using Project Professional.
- Open Credential Manager (via Control Panel) and go to:
- Windows Credentials > Office 365-related entries
- Remove any stored credentials associated with Office 365.
- Reopen Project Professional. When prompted, enter your credentials carefully and press OK.
Advanced fix: Clear identity records from the windows registry
Important: The following steps should be carried out by someone with administrative access and a working knowledge of the Windows Registry.
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In Project Professional:
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Go to File > Info
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Clear all managed accounts except for Computer
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Open Registry Editor (RegEdit) and navigate to:
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity\Identities -
Review each entry to identify the Office 365 account.
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Delete the registry key associated with the Office 365 identity.
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Close the Registry Editor.
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Open PWA in the browser and attempt to edit the project using Project Professional.
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You should now receive a fresh prompt to enter your credentials.
What to do next if issues persist
If you’ve followed the steps above and continue to experience problems:
- Verify your Microsoft 365 account is fully licensed and not blocked or deactivated
- Ask your IT team to verify domain trust, firewall settings, or SSO configuration
- Ensure you’re using a supported version of Project Professional (2016 or later)
For advanced troubleshooting, refer to Microsoft’s documentation on Project Online user access and troubleshooting.
Summary
Whether you’re encountering browser-based edit failures or authentication issues with Project Professional, the most common causes are blank lines in schedules and cached credentials. Thankfully, these problems are typically easy to resolve with the right steps.
For teams that frequently collaborate across complex schedules, maintaining clean plans and monitoring credential behaviour can reduce disruption and help keep projects moving.
