Page not redirecting properly

Just today I have started getting this message when going to SOME of my catalog and product pages:
"Firefox has detected that the server is redirecting the request for this address in a way that will never complete." So I tested on three different browsers and a few computers. Errors on all. Not ALL categories, not ALL products. Some of the problem pages:
Categories:
http://www.photoimprints.com/beverage-insulators-c-15.html
http://www.photoimprints.com/id-and-luggage-tags-c-8.html
http://www.photoimprints.com/calendar-products-c-21.html
Products:
http://www.photoimprints.com/custom-magnet-p-27.html
http://www.photoimprints.com/custom-mouse-pad-p-20.html

I have changed absolutely nothing in any files since it was last running correctly.

I isolated the problem to the SEO URL's by turning it off and things worked. I then worked down each SEO setting making changes and testing. When I got to "Enable Automatic Redirects" and set it from TRUE to FALSE, my pages started working again.

So... can anyone suggest why I had this problem with no changes on my part? It's hard enough to fix things that stop working when you make changes, much less when you don't!
Thanks!