Pulled the following from another forum and it seems to work: "This worked for me....Strange, looking back, I did exactly what my IPAD told me to do...but the error on the screen was not clear.
1. login to Itunes from your computer
2. Verify that your device is connected. If not, resolve that issue.
3. Go to Store from the menu bar, and select Search
4. Search for the same application you were trying to install on your Ipad.
5. From here, I don't recall the exact steps, but it was easy, just follow the prompts. In my case, this happened when I changed my password in Paypal. I had to "reaffirm" it was me, authorizing the payment. Thank you Apple, for taking care of me, again.
Thank you OrangeMarlin, for forcing me to "read my screen". I am bugged however, by apple not answering these forums/creating error messages that are clearer and more "user friendly"
The thread in its entirity:
https://discussions.apple.com/thread/2567347?start=45&tstart=0