Pro Sites trouble... no redirect to checkout?

When I log on as a new user, and it brings that user to the upgrade to a pro site page, i select a payment plan (monthly, it turns red) and then click the paypal checkout button, it starts to load and then does nothing? it just reloads the same page the user was just on regarding the payment options.
Any idea why this might be?
I just disabled all plugins except the pro sites plugin and it still is responding the same.

A login you can use to see this is here:
user: roofoo
password: roofoo
the error is found here:

Any help is appreciated!