! Apple store cannot be opened because of a problem

I bought a new MacBook Pro this week. It's all going well until last night. When I switched it off a message popped up saying 'software updates are available for this MAC do you want to install before shutting down'

I clicked yes - but then panicked because I worried that I didn't know what the updates were so I forced-quit in the middle of the installation. What an idiot you are thinking - you are right. I don't even know why I did it (I don't want dodgey things downloaded on my MAC from the internet but obviously over-thought this one... I was having a busy day).

Now I can't get into the Apple store to install the updates (turns out they are for my OS Mountain Lion - OS X 10.8 (12A269)

I also can no longer access i-Tunes.... What a wally.

Here's the message I'm getting:

! Apple store cannot be opened because of a problem

"Check with the developer to make sure App Store works with this version of OS X. You may need to reinstall the application. Be sure to install any available updates for the application and OS X."

All help would be greatly appreciated.