500 Error with Pro Sites Stripe Gateway

Hi, I'm working on setting up a dev server. When I change the gateway in Pro Sites to Stripe I get a 500 error at the front- and back-end (site completely disabled). I don't see anything in the error log. Below is from the access log. Only way I've found to resolve it is to delete the plugin. I suppose something is not configured properly on my server, but I don't know where to start.

"GET / HTTP/1.1" 500 20 "-" "Mozilla/5.0 (Windows NT 6.1; rv:15.0) Gecko/20100101 Firefox/15.0.1"