Consulte KB979281 , isso deve explicar o que está acontecendo e como resolvê-lo.
This issue occurs if you back up a library that contains custom folders that are located under your user profile.
To resolve this issue, take one of the following actions:
Move the library folder from the user profile path to a location outside the user profile path. For example, move the folder to the C:\MyLibraries folder.
Exclude the library from the list of files that Windows Backup backs up. Then include the original location of the content in the library in the backup list.
Move the library folder to a location other than the user profile folder. Then, add a link to the moved folder from the library. Make sure that the library is included in the backup.