Sagepay Server - 5006 error

During test transactions I'm getting this -
"Server error 5006: Unable to redirect to Vendor's web site. The Vendor failed to provide a RedirectionURL."
and
"HTTP error 500: The request was unsuccessful due to an unexpected condition encountered by the server."
I'm on 2.3.0.2 I've sent a support request to see if my host is blocking Sagepay's IP addresses other than that i'm stuck because i can't manually enter any URLs in the payment module.
Has anyone com across this?

OK another reply to self. Top tip, don't have the site in maintenance mode for test transactions.