One of our customers were getting below error while editing Project Site Page. Below are the steps to reproduce the issue.

  1. Open the Project Site
  2. Click on Page >> Edit page
  3. Error

Error:
An unexpected error has occurred.

Web Parts Maintenance Page: If you have permission, you can use this page to temporarily close Web Parts or remove personal settings. For more information, contact your site administrator.

In the ULS log I found the following entry.

System.InvalidOperationException: The Visible property cannot be set on Web Part ‘g_310a7bdb_0bbc_4d51_a7ad_48894810d5d8′.  It can only be set on a standalone Web Part.

The above error indicated the issue with Visible Property of the webpart. However there was no changes made to any of the webpart.

The project site contained below three web parts.

  1. Project Summary
  2. Document
  3. Site Feed

Site feed is not the OOB webpart for the Project Site, so I removed it by accessing the webpart maintenance page for the site and that helped to resolve the issue. I followed the same steps for all other affected sites to fix the issue.