Trouble with Image Link URLs

Hello,
I am building a portfolio site and ran into trouble with linking image thumbnails to their attachment link pages. It all worked fine when I first added all the thumbnails and linked them to the image pages but then all of a sudden it didn’t work, I’m not sure why, and I just get “Page not found” when clicking on the thumbnails- see for yourself! http://cathydurso.net/?page_id=202

I’m using the Twenty Eleven theme. Any suggestions on what to do? I didn’t change any of the permalinks or anything, they are set to the default urls.

Thanks in advance.