Can't update an app -- help? I can't update a particular app (CSR Racing) -- when I go to the "Updates" part of the app store or to the app itself and tap "update", it will go to the progress bar thing (circle with square in middle) for a split second, then go back to showing "update".  Now it's just sitting there with the progress bar not doing anything.  Help meh!

I already restarted the iPhone and tried to reset the App Store (as proposed by @csstudent in one of the answers), it still won't let me update it.
Type any one of the five bars at the bottom of the App Store (Featured, Top Charts, Explore, Search, Updates) 10 times in rapid succession. You will see the page redraw itself. This is a little-known feature in iOS that resets the App Store on the device. Try this, and then try to update the app.