Problems logging in with Membership 2 plugin

I have a custom login form that I'm using with Membership 2 and I keep getting an AJAX error that is preventing me from logging in. Here's the error from the Console (sorry it's vague):

Object {readyState: 4, responseText: "", status: 500, statusText: "Internal Server Error"}

I can give you a sample login to try through a pm. Any help or insight you can lend would be much appreciated!