Hello,
When you find a warning in the Event Log that states that Auto-Protect did not load. Event ID 22: "Symantec AntiVirus Auto-Protect failed to load", there are multiple causes for this error, but most commonly there could be a problem with the virus definitions failing to load.
Uninstalling and reinstalling will often resolve the virus definition issue.
However, Try this first
'How to clear out corrupted definitions for a Symantec Endpoint Protection Client manually.'
http://www.symantec.com/docs/TECH103176