Well the windows error 5 = Access is denied. So it looks like SpySweeper is either protecting that file or possibly folder.
If you do a search for masters.mst
http://www.google.com/search?q=masters.mst, you will see lots of hits relating to access denied. I think that file has something to do with the signatures, so it may be worth excluding that file from scanning, the decision is yours. But, there should be no additional impact as the file can't be scanned because access is denied.
Standard Shield, Customize, Advanced, Add and
Program Settings, ExclusionsAdd this path.
C:\Program Files\Webroot\Spy Sweeper\Masters\masters.mst
Or C:\*\Spy Sweeper\Masters\masters.mst using the wildcard * to shorten the path.