We've been hearing from some people that they've had trouble updating. As far as we can tell, this is due to some kind of mishap on Apple's update servers, and we're doing everything we can do address the issue.
If your iPad is stuck on the update, deleting and reinstalling iMPC will correct the issue. To prevent losing custom samples and sequences, follow these steps:
Step 1: Connect your iPad to your computer.
Step 2: Launch iTunes on your computer, click your iPad at top, click "Summary".
Step 3: Click "Back Up Now". Wait for Backup to complete.
Step 4: On your iPad, delete iMPC by tapping and holding the icon on Home Screen.
Step 5: On your iPad, install iMPC from the App Store (this will be a free install).
Step 6: (optional) On your computer, in iTunes, click "Restore Backup..." This will restore any custom sequences and sounds.
Check our twitter and facebook for discussion/updates as well. We'd like to hear from you if you're having trouble.
Lots of people have been posting negative App Store reviews (and rightly so) about the stalling update. It's heartbreaking for us because it's out of our hands since we believe this is an Apple server glitch. If you're an iMPC fan, we'd really appreciate you supporting it with a review on the App Store! Peace — JP