it can be due to corrupt definitions on this client
Stop SMC server (smc -stop)
Delete The dated folders abd temp folders in progra files\Common files\Virusdefs
doc 7 set..\all users\app. data\syamntec\liveupdate\downloads
Delete all the contents of the download folder.
Download and update this client using Rapid Release then it should retrive the deifintions automatically.
ftp://ftp.symantec.com/AVDEFS/symantec_antivirus_corp/rapidrelease/
and download
symrapidreleasedefsi32.exe