Can't download and apply updates

All,

I have various updates that need to be applied to my Mac Pro running OS X 10.8.2. When I attempt to download and install updates, one of two things will happen:

1. Half way through - the download will stop with an error message like "Can't complete the download"
2. (And this is the current situation) The App store will say I have no updates available - even though I know several are available

I have tried a few of the tips I have already found in this forum:

• I have been into the Spotlight settings and attempted to reindex many of my files
• Tried to delete /Library/Caches, ~/Library/Caches, ~/Library/Cookies, /Library/Preferences/SystemConfiguration/NetworkInterfaces.plist and ~/Library/Preferences/com.apple.storeagent.plist. Doesn't work. Actually, some of these files aren't on my Mac
• Checked my iTunes account - it's fine
• I can buy new apps just fine - just can't apply updates to existing ones
• I did go to the iTunes download page and successfully installed iTunes v11. Just can't get it to work throught the App store

Not sure what else to try. Here's a screen showing that my Mac believes there are updates available but the App Store says no.

Any other thoughts?

Thanks