The "xfer" and "xfer_temp" folders still store files scanned by AutoProtect transferred from migrations of legacy Symantec AntiVirus (SAV) or SEP installations".
To be honest it seems that for some unexpected circumstances (for example a damaged file) SEP starts a loop where a file goes in quarantine (.vbn archives), then it is extract this file in a .tmp file to rescan it, it is again detected and quarantined, and so on...
Try re-installing sep client and check .
& check article below for 12.1 http://www.symantec.com/business/support/index?page=content&id=TECH102953