Connection error when trying to submit payment

I'm using Gravity Forms for my user registration form. The registration process works fine but after I choose my membership and click the submit button, the page hangs and then I get an err_connection_timed_out error (see attached). Same issue in Firefox.

I have Authorize.Net set up. I've tried this is in both sandbox and live mode with the same result.

I have no idea what to do to trouble shoot and fix this. Can someone help?