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SharePoint 2010: Webpage message: An unexpected error has occurred

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Problem

A site owner reported that he was unable to edit the home page of his SharePoint 2010 site after it had been moved to another site collection in the same web application.  When he clicked on the Edit button on the Page ribbon, he experienced a  "Sys.WebForms.PageRequestManagerServerErrorException: An unexpected error has occurred." webpage message

The user's account was a member of the site's owner group.  A site collection administrator was able to edit the page without issue.

Troubleshooting

Adding the user's account to the Site Collection Administrator's group enabled the user to successfully edit the page.  This outcome suggested that the problem might be permissions-related.

Document library containing the home page, SitePages, was found to inherit its permissions from the parent site,

SharePoint Server Publishing Infrastructure site collection feature was found to be activated.

User's account was found to have at least read permission to the Master Page Gallery document library.

User's account was found to not have any access permission to the Style Library.  Granting read access had no affect.

User's account was found to not have any access permission to the Web Part Gallery.  Granting read access enabled the user to edit the page.

Solution

If SharePoint Server Publishing Infrastructure site collection feature is activated for the parent site collection, ensure that the user has at least read permission to the site collection's Web Part Gallery document library.

References

Notes

  • Only Web Part Gallery permissions were found related to this problem.  I could remove permissions to the other key document libraries without impact.
  • This problem was found to occur for SharePoint 2010 but not for SharePoint 2016.