Hello,
In this case, there are few questions and we would require certain logs to get to the bottom of the issue.
Question: What Operating System is the SEP client on and SEPM on ??
Are there any GUP configured?
Please Collect the Sylink logs from 1 of the SEP client machine which you think should be updated.
http://www.symantec.com/docs/TECH104758
Suggestions: Incase, if the SEP clients are windows 2008 or Windows 7 or Windows Vista machine, please disable the User Account Control Settings and restart the machine and check again.
Hope this helps!!!