MU Domain Mapping - 404 - 403 - HTTPS/HTTP - SSL

Hi

I created a multisite on the Mediatemple Grid. Everything working fine, using Gravity Forms for the sign-up process.

Having issues with the domain mapping. Created a test user and tried to map a domain. The admin shows https and when I try to add the domain I get 403/404 errors. It must be something to do with the https, I presume.

Is there a way to fix this, so users can add http domains or anything else you might suggest?

Your replies appreciated.

Richard