I encountered this problem after my client had changed the administrator password on his server. His virus definitions were three weeks out of date before he bought the issue to our attention.
To resolve the issue I did the following:
1. Unchecked the "Enable LiveUpdate" box on the LiveUpdate configuration page and saved the changes.
2. Restarted the Symantec Mail Security for Exchange service.
3. Checked the "Enable LiveUpdate" box on the LiveUpdate configuration page and saved the changes.
Check the events in your scheduled tasks to make sure the events have been recreated with the correct security permissions.
Of course, you can probably just change the password in the scheduled event, but as this was not the process I followed, I cannot guarantee its success.
See the link to "Symantec Support Document ID:2004031510084454" for details on resolving this problem.
Got this message when Symantec Mail Security for Exchange was trying to automatically update virus definitions. When there was no update found an error was generated.