After losing all of the GPO backups due to the backup share location specified in the Storage configuration failing, GPOs can no longer be checked out, restored, view the history, etc as the following error is thrown:
"Error retrieving backup"
Specify a new share as the Storage location for GPO backups:
Once a new storage location has been provided, all of the GPOs will need to be unregistered from GPOAdmin and reregistered. When you reregister you can select the option to 'maintain version history'. This will maintain the version number of the GPO as viewed from the GPOAdmin client. This will also allow you to still see the revision dates and comments in the History of the GPO. As the backup files for those different revisions are gone, you will not be able to view the settings that were configured for each older version nor will you be able to rollback to a previous version.