Avamar: File System and Windows VSS Backups Fail with "INTERNAL ERROR" | Folder Redirection

Backups targeting the C:\Users or C:\Documents and Settings directories fail with errors similar to the following:

avtar Warning <6772>: Unable to set uevent object - 'code 6: The handle is invalid'
avtar Warning <6777>: Cannot translate path '' to full path, proceeding with original path
INTERNAL ERROR: <0001> assert error (mtPath.numelems() > 0), upath_win.cpp line 704
avtar Error <5137>: Unable to open "" for backup (code 0: success)
avtar FATAL <0000>: Backup not sealed due to previous errors
avtar FATAL <5155>: Backup aborted due to earlier errors. No backup created on the server.

If debugging is enabled (using the dataset or avtar.cmd in C:\Program Files\avs\var), additional messages may appear: 

2022/03/16-15:57:08.82100 [avtar] upath_win::translate_path translating 'C:\Users\ADM-DELLEMC\.AppData\.Data\.Data'
2022/03/16-15:57:08.82100 [avtar] GetReparsePointInfo(C:\Users\ADM-DELLEMC\.AppData\.Data\.Data) called
2022/03/16-15:57:08.82100 [avtar] upath_win::DoTransPathPrepWork detected reparse-point, using lookup path: \\Avamar.com\documents$
2022/03/16-15:57:08.82100 [avtar] upath_win::translate_path looking for translation for '\\test.Avamar.com\documents$\'
2022/03/16-15:57:08.82100 [avtar] upath_win::translate_path WARN mtpath lookup failed (\\test.Avamar.com\documents$)

The affected folders are configured with folder redirection, which causes Avamar to encounter reparse points that it cannot resolve during backup operations. 

Example:

 
 

To work around this issue:

1. Log in to the redirected target system using either:

   • A Domain Admin account, or
   • A user account whose profile is affected by folder redirection.

2. Investigate folder redirection settings:

   • Review Group Policy Objects (GPOs) or local policies that apply folder redirection.
   • Check the security permissions on the redirected folders to ensure that the backup agent has access.

3. Adjust backup dataset (if applicable):

   • Exclude redirected folders from the backup dataset if they are not required.
   • Alternatively, configure the dataset to explicitly include the redirected path.