Cant RDP Vista Business from Ultimate x64

I am trying to use RDP from my Vista Ultimate 64 bit desktop machine to control my vista business laptop but when i start the RDP and enter the username and password it responds with "Your credentials did not work".
I have successfully connected to other XP machines from the ultimate 64 machine and i have successfully connected to the business laptop from xp machines which hint towards there being an issue between these two machines only.
Any Ideas?

Remote desktop set to "Allow connections from computers running any version of remote desktop".
No users selected as the only user set up, is a member of the administrator group.
Laptop and desktop are not members of a Domain.

Still no joy

Yep, but do you use on the 2 systems the same name?

The computer settings are as follows:

Vista Ultimate x64
Computer Name: main
Full Computer Name : main
Workgroup: WORKGROUP
User name: paulie


Vista Business x32
Computer Name: LT015a
Full Computer Name: LT015a
Workgroup: WORKGROUP
User Name: paul

The weird thing is after your comment about the names being the same i checked the user accounts and clicked the "configure advanced user profile properties" and noticed there is only one entry in here for LT015a\LT015, with this i tried the RDP again entering the LT015 instead of paul for the user name and it worked fine.

So still a bit confused but over the moon as your help has sorted my problems out.
Thank you

Great, glad you sorted it out