SBS 2011 Cant connect to PC's using RWA site, keeps asking for password

Hi All,

have carried out several SBS 2011 installs now. but have come up against a problem on the latest install with not being able to connect to a PC on the LAN from using the RWA site. Users are configured for RWA site access, and can login to OWA site and RWA site without issue. When the connect to computer option is used the user is promted for their username and password and the box goes off and attempts connection, only to come back with the logon attempt failed.

Checking security logs, can see 4634, 4648 and 4624's which reference the user, but all are audit success. no failures, the 4634 mentions the logon session being destroyed, but i cant see why!

There is a 3rd party signed SSL cert installed for RWA and OWA which is happy and in use for Active Sync and Outlook Anywhere for the same and other users on the network.

I have checked the RD Gateway manager (using the MS method of cmd line access and ignoring the warnings about SSL certs not installed etc) and all looks ok in there too.

Can anyone suggest where to look at all, i have hunch its going to be in the IIS manager somewhere and probably a random tick box for authentication too...

Thanks in advance.