Hello,
What version of SEP 11.x are you running?
On what OS have you installed the SEPM on?
Are you running Proxy ? Could you run the liveupdate from the Run window and check Error do you receive?
START > RUN > Type "luall.exe" (without quotes) > click OK.
Could you please upload the Log.liveupdate to us?
For Troubleshooting, here are following few Articles:
1) How to Uninstall and Reinstall LiveUpdate When a Symantec Endpoint Protection Manager or Symantec Endpoint Protection Client is Installed (SEP 11.x)
http://www.symantec.com/docs/TECH102609
2) LiveUpdate and content troubleshooting for the Symantec Endpoint Protection Manager
http://www.symantec.com/docs/TECH105924
3) Symantec Endpoint Protection: LiveUpdate Troubleshooting Flowchart
http://www.symantec.com/docs/TECH95790
VIDEO:
Troubleshooting LiveUpdate Part 1
Troubleshooting LiveUpdate Part 2
Troubleshooting LiveUpdate Part 3
Hope that helps!!