Hello,
Are you logged in as an Administrator??
There are few Suggestions:
1) Check Your Hard Disk for Errors
- Click Start, click Run, type cmd in the Open box, and then press ENTER.
- At the command prompt, type chkdsk /f, and then press ENTER. And check Automatically fix file system errors.
2) Try uninstalling SEP via SEP CleanWipe Utility. (to get the Utility, you may have to create a case with Symantec Technical Support) OR
3) Follow the Manual Uninstallation Steps provided by Thomas above.
Hope that helps!!