500 error on theme (not wpmudev theme)

I just got a theme for my site, and upon enabling it, I get a 500 error. What are the most common problems that cause this on a new theme? Other themes work fine. I have read a bit about TimThumb issues, but this does not seem to cause the whole site to shut down. The only recovery is to remove the theme from the directory and allow WP to automatically switch to the default (since the admin areas break, as well as network). I realize the theme author should fix this, but I am on a time crunch and need to expedite getting this working. Thanks.