Hi Fred, see if this helps...
Post subject: NSURLErrorDomain error -1100 in OS X 10.8
If you check for software updates using the App Store in OS X 10.8 and get "NSURLErrorDomain error -1100" the problem may be with your Software Update preferences. This is particularly likely if you were using a custom Apple Software Update server. To solve the problem, quit the App Store, move the following two files (if present) to the trash, restart, and only then rerun App Store updates: