Help with domain mapping

Ok, so here is a summary of what I am trying to achieve:
I have a wordpress multisite and I would like to map the sub-blogs within it.

The domains that should be mapped to these sub-blogs are on a different hosting server from the wordpress Multisite.

While attempting to map one of the domains, I have hit an issue. I have entered in the url for the domain into the sub-blog and changed the A record of the domain to the ip address of where the wordpress multisite is and what happens after all of that is this -

I'm not sure what I'm doing wrong.

Could you please help in any way possible.

Thank you