i am having one domain in single forest with two active directory forest,all the domain controllers are running windows 2003 sp1 with windows 2000 native mode,i am having exchange 2003 running in the domain and i want to migrate to exchange 2007. i applied all the active directory and schema modifications and in exchange 2003 the default exchange 2007 routing group also displays,i need to install client access,unifed message and transport role in one server and mailbox role in cluster.when i tries to install exchange 2007 with client access,unifed message and transport role i got an error message stating could not find active directory site where this computer belongs to,after several way of trouble shooting i make this computer domain controller and the installation of exchange server 2007 went of fine,then when i tried to install mailbox role in cluster server the same error message received?so my installation is in half way and i suspect its a problem with dns server ? please help me to solve the problem,

i suspect if you investigated your AD Sites & Services topology you would find the problem in there somewhere, something to do with the IP subnets / sites they linked to & domain controllers which are assigned to those sites...