Vmware backup failing

Hi,

    M trying to configure backup through new v center version 5.5.(nbu 7.6.0.2) but the backup is failing with error code 23 Error opening the snapshot disks using given transport mode: Status 23 . I have tried nbd method but backup still fails .My concern while analysing logs i came across path  C:\Program Files\Veritas\NetBackup\online_util\fi_cntl. There are many xml ,bid ,0 files of the  failing VM what are these files and whether it is related to backup getting failed.