I'm sorry that you have been unable to add images to your library. I do see that you have plenty of space in the library at the moment. Unfortunately, I was not able to replicate the issue you're experiencing. We definitely want to help out, but need some more information to do some testing.
Would you mind emailing us at Social_Support(at)ConstantContact(dot)Com, with a screenshot of what happens and any other details you may have? Are you using the mobile app or desktop webpage? Please reference this post in your email, and we will be sure to correspond with you as we test.