Select Users Can't Submit Photos

Hello everyone. I have an issue that is sort of driving me nuts.

Some of my users are having trouble submitting photos to my website. I am using a photo contest plug in that requires users to register, retrieve their password from their email, and complete log in before submitting. Some users are saying they are being directed back to Facebook when clicking on the “Add Photo” button, which makes no sense to me, while others are saying that nothing is happing at all when they click the button. And then some users are able to submit without issue.

I am not sure if the problem is with the plugin or with wordpress. I received a few messages before i started my contest with a different form plug in that their submissions weren’t working, but not nearly as many as now. Any suggestions? Thanks.