Adding to domain with a different subnet

Hi ,
I am having problems adding a machine to a domain with a different subnet to the PDC.
I can ping both controllers from the machine in question.
The user account details are correct and I know this is possible but each time I try to add it Iget the error that “Unable to connect to the domain controller for this domain.Have your administrator check the computer account on the domain” when I enter the username and password I get “Unable to connect to the domain controller for this domain.Either the username or password is incorrect”
All ideas would be appreciated,
Thanks!