Server is up to date but client system is out of dated.
How many clients are the problem?
Remove the defintion contents and update new one.
Defintion corruption shall be the reason of out of date.
It's managed or unmanged client ? What happend when you have select fix or select liveupdate Tab ?
You can run symhelp tool and identify defination corupted or not.
http://www.symantec.com/business/support/index?page=content&id=tech170752
Have you performed any basic troubleshooting yet? I'd recommend following this article:
I was tried to fix it 2 times after a hour no update.
Client is server connected.
I followed the article http://www.symantec.com/docs/HOWTO59193
If the problem will be not resolve then run symhelp.
Enable sylink debugging if you wish, post the log here for review.
What did symhelp show? Definition corruption?
A single system problem which resolve with article http://www.symantec.com/docs/HOWTO59193