My problem is similar to the one mentioned above, but not the same .. ->
BackupTapeFile::SkipFileMark: SetTapePosition failure on backup device '\\.\Tape0'. Operating system error 21(error not found).
This backup job was runing fine too for a long time, and for 3-4 day its making me crazy.
The scheduled evening backup is faling, but if i run a "manual" backup it's working fine..