I don't know if this helps anyone, but I think I fixed the problem...
A previous coder did a header redirect to
http://www.whyrentbooks.com when the URL request was
http://whyrentbooks.com. He didn't realize that he could prefix the domain in the configure.php file. I went ahead and did that, and somehow it must have either 1) conflicted with his code 2) conflicted with something else in the site.
I know this doesn't really solve anything, but if anyone is having a similar problem, try to remember the changes you've made to your configure.php as this may be the source of the problems.
Luckily I have an SVN system so I can see all changes that were made.