iPhoto stopped recognizing my iPhoto library, and it will not let me click open when I find the library in my files. Suggestions?

I have seen similar questions--mostly from 4-6 years ago--but none are quite the same as mine. I tried to export a photo from the web to iPhoto for editing and received a message stating, "Which photo library do you want iPhoto to use? To open, iPhoto needs a photo library. Select a library from the list, find another library on your computer, or create a new library that you can import photos to later. The same photo library will be used the next time you open iPhoto." Below this is a empty box. Below the box there are three buttons: [Other Library...] [Create New...][Choose]. Since the box is empty the [Choose] button is grayed out. If I click [Other Library...] I can go to Pictures->iPhoto Library. I can highlight iPhoto Library by clicking on it, but nothing happens when I click Open at the bottom of the window or if I double click iPhoto Library itself.

I only have a handful pictures on this machine--MacBook Air, OS X 10.9.4, 96 GB memory free--so I could create a new library without much pain, but I hesitate to since I don't know what caused the problem in the first place. Any ideas?

Thanks.