Have a Mac Pro early 2008 and trying to update from the App Store and get the following error message, "The operation couldn’t be completed. (NSURLErrorDomain error -1012.)" Anyone else encounter this problem and know how to fix it?

No, trying to obtain updates from the App Store. The App Store isn't installing or offering any updates for my OS X and when I click on the update button I get that error message. I have had to update iTunes from the Apple website but I can't do the same for security updates or the most recent Safari updates. What I have done so far: cleared the caches to see if something in there was causing the problem; booted into restore mode and checked the hard drive and there are no problems; erased the hard drive and restored from a time machine backup.

Still stuck.