Can not join my domain

Hi all,
I have an ASA 5510 Cisco and 3 3750 Cisco Switches which We have configure them to 3 different subnet. 10.10.12.0, 10.10.10.0 and 10.10.11.0.On my server 2008 I have my domain Controler .11 subnet and a client as well. I was able to join that domain with no problem. My problem is when I am trying to join a client from my .12 subnet. I can ping across my two networks. It is this a DNS issue? If it is, how can identify on my server that I have in fact a DNS issue?.
Thx