If you are facing with an error like the following:

4/27/2009 4:59:32 PM – Critical bpbrm(pid=7716) from client test.local: FTL – snapshot creation failed, status 156
4/27/2009 4:59:32 PM – end Flash Backup Windows , Create Snapshot; elapsed time: 00:00:08
4/27/2009 4:59:32 PM – end writing
Status 156

When you look at the bpfis logs you can see a log like this:

16:59:30.699 [5512.6280] <2> onlfi_vfms_logf:     [2009-04-27 16:59:28.840 'SOAP' 6504 trivia] Sending soap request to [TCP:test.local:443]: GetSummary

16:59:30.699 [5512.6280] <2> onlfi_vfms_logf:     [2009-04-27 16:59:29.043 'SOAP' 6504 trivia] Received soap response from [TCP:test.local:443]: GetSummary

16:59:30.699 [5512.6280] <2> onlfi_vfms_logf:     [2009-04-27 16:59:29.043 'SOAP' 6504 trivia] Sending soap request to [TCP:test.local:443]: GetSnapshot

16:59:30.699 [5512.6280] <2> onlfi_vfms_logf:     [2009-04-27 16:59:29.262 'SOAP' 6504 trivia] Received soap response from [TCP:test.local:443]: GetSnapshot

16:59:30.699 [5512.6280] <2> onlfi_vfms_logf:     [2009-04-27 16:59:29.262 'vcbMounter' 6504 info] Scanning snapshot _VCB-BACKUP_

16:59:30.699 [5512.6280] <2> onlfi_vfms_logf:     [2009-04-27 16:59:29.262 'vcbMounter' 6504 info] Found match: snapshot-1847

16:59:30.699 [5512.6280] <2> onlfi_vfms_logf:     [2009-04-27 16:59:29.262 'vcbMounter' 6504 error] Error: Backup snapshot already exists.

16:59:30.699 [5512.6280] <2> onlfi_vfms_logf:     [2009-04-27 16:59:29.262 'vcbMounter' 6504 error] An error occurred, cleaning up…

16:59:30.699 [5512.6280] <2> onlfi_vfms_logf:     Deleted directory c:netbackup_vmware_mnttest.local

The reason can be a remaining snapshot that vmware couldnt remove successfuly on a previous backup attempt.

Try to remove that snapshot from the server  and retry your backup.