I had that issue with a friend today.
I found that when the apps cannot be opened, you go to apps store and load a new app it solve the problem. But was not a good solution.
I connected the ipad to his laptop. I found that the ipad has was not authorized on the machine. I did the authorization, transfer purchases, back up, sync, etc.
So far the issue was not repeated and I cannot confirm yet if this was a final solution. If the issue doesn't repeat again I will let you know.
If this solve your problem, please post.