How to remove a small black window that appears on the upper right corner of my iMac and covers everything behind it every time I open iPhoto?

Every time I open iPhoto on my iMac a small black window appears in the upper right of my desk top and covers everything behind it, including iPhoto. The window says "Blocked Plug-In". I cannot move it, delete it, force quit it, etc. I have quit iPhoto, but the black window remains. I have restarted and shut down the computer, but when I open iPhoto the black window comes back. I have right and left clicked on the black window, but I cannot get rid of it. How do I stop the black window from appearing on my screen?