Hello,
Firstly, edit the proxy settings on SEPM, set the proxy server settings. Login to SEPM > Admin > Servers > Highlight Local Site > Edit Site Properties > Liveupdate
Also try following the below steps.
Launch the Windows Control Panel and
- Open Add or Remove programs and click the Add/Remove Windows Components button.
- Disable the Internet Explorer Enhanced Security Configuration option, and then click Next.
- Upon completion of the Windows Components Wizard, click Finish. You may need to restart the computer for the changes to take effect.
It could happen that maybe the LiveUpdate catalog or the SEPM installation is damaged.
1) If it is a very fresh installation, just wait some hours
2) Reinstall LiveUpdate without saving the catalog but re-creating it:
http://www.symantec.com/docs/TECH102609
3) Repair SEPM from add/remove programs
If the clients are already up-to-date, it means that they are taking the definitions from another source.
Hope that helps!!