After changing your password of your Office 365 account, your credentials used in Microsoft Project also need to be changed.

To fix this:

  1. Open MS Project
  2. Open a blank project
  3. Click the ‘File’ button at the top right (as if you were to save a document).
  4. Then click ‘Account’, which is almost at the bottom of the menu.
  5. If the incorrect account is shown, click ‘Switch Account first’.
  6. Then click the ‘Sign Out’ button for the account you use with Project Server as shown in the picture below.
  7. Then enter your credentials again when trying to open a project from Microsoft Project Server.

Note: This will not work if you are using the same account to log in to Windows.