For anyone who comes across this problem, which I did tonight on my laptop, you may want to first try closing Software Center and re-opening it. Several suggestions on askubuntu.com and other results from searches online mentioned removing entries from the source lists and so forth. As I said, just closing and re-opening solved the problem where it happened to me. I’m not going to assume this is something new, as people asking about it on those sites when I searched it were experiencing it with 12.04. I never experienced it in 12.04 and have only experienced it once so far on one machine running 14.04.
What occurred was when clicking on an application in the Software Center I was shown no reviews or info for the application, but instead only the message Available from the “main” source with a button saying Use This Source where Install would normally be.