Incorrect checksum ending with status 84
I have a windows 2008 r2 server that during backups get thats getting errors. I've made sure VSS was ok and services were running. We have netbackup appliance and the client is 18.104.22.168. This error sometime will just clear up the next day and sometimes it is consistant for couple of days. We dont use tapes, just disk. I dont know what may be causing this or even where to look. Here is the part of the log that shows 1st error.
any help is appreciated.
08/23/2012 10:37:42 - Info bptm (pid=31377) backup child process is pid 31400
08/23/2012 10:37:42 - begin writing
08/23/2012 10:37:49 - Info bpbkar (pid=178184) change journal NOT enabled for <C:\>
08/23/2012 10:38:29 - Critical bptm (pid=31377) A portion of data to be included from a previous backup (backupid = stx.xxxxx.com_1345609030, offset = 3568915456, length = 512) has incorrect checksum (calculated checksum from backup image ea7dcdefc0a77ac7e171401e2972c6118a367130, expected checksum 75da22ad4d037861df57c4b1404f5026751f152d)
08/23/2012 10:38:29 - Critical bptm (pid=31377) image write failed: error -1: plugin error
08/23/2012 10:38:31 - Error bptm (pid=31377) cannot write image to disk, Invalid argument
08/23/2012 10:38:32 - Info bptm (pid=31377) EXITING with status 84 <----------
08/23/2012 10:38:32 - Info primaster (pid=31377) StorageServer=PureDisk:primaster; Report=PDDO Stats for (primaster): scanned: 3352783 KB, CR sent: 184385 KB, CR sent over FC: 0 KB, dedup: 94.5%, cache hits: 0 (0.0%)
08/23/2012 10:38:52 - Info bpbkar (pid=178184) done. status: 84: media write error
08/23/2012 10:38:52 - end writing; write time: 0:01:10
media write error (84)