Here is a workaround:
1. Stop all Symantec Endpoint Protection services
2. Delete all .tmp files and folders in C:\Program Files\Common Files\Symantec Shared\SymcData\sesmipsdef32, \sesmipsdef64, \sesmvirdef32, and \sesmvirdef64
3. Delete the contents of the C:\Documents and Settings\All Users\Application Data\Symantec\LiveUpdate\Downloads folder
4. Restart the SEP services
The SymDelTemps utility could also be used to delete the temp files in the sub-folders. Please be aware that the behavior will continue if the utility is used without stopping the SEP services.
The guide above is essentially what the SymDelTemps utility does. So if you don't want to call support or don't have a valid license you can do this instead. Keep in mind this is strictly a workaround and the upgrade to RU5 should fix your issue. Feel free to post again or PM me directly with any further questions.
Thanks
Grant