Unfortunately any issues connected to updates or purchases on the App Store are things that Apple can answer better than we do. Taking a look at this thread might help you:
Hope it helps,
Just wanted to inform you, that it still doesn't work. I tried everything in the thred. Nothing seems to work. Please assisst. Thank you
Sent from my iPad
Have you tried to update from iTunes?
Just an idea, but you might upload any projects that you wanted to save to the Creative Cloud storage through PS Touch and then just uninstall and reinstall the app versus attempting to update. I would also want to confirm you have ample free space on the device. If you are not able to install an app you purchased you could contact Apple support for assistance.