OnPostRestore error might be caused by SharePoint Cache
If you get OnPostRestore error during restoration process in SharePoint, one of the things that you might need to do is to clear SharePoint cache
- Go to Services and stop Windows SharePoint Services Timer service
- Go to C:\ProgramData\Microsoft\SharePoint\Config\GUID directory
- Create a copy of cache.ini file
- Edit the cache.ini file and change the number to 1
- Delete all the xml files
- Start Windows SharePoint Services Timer service
