EMC Retrospect 7.5 errors

hi have recently changed our backup script, but when we try backing up the network drives on a dfs share we get errors –

MapError: Unknown windows error 1,920
TPCFolderLoc::Startfind: UGetInode failed, \\?\GLOBALROOT\Device\HarddiskVolumeShadowCopy121\
blah blah blah winerr 1920, error -1001

we get 5 of those followed by compare errors (with no error code) but 99.9% of the files are image files.

any ideas? have tried talking to EMC but its like banging your head on a brick wall

thanks in advance