DNS is most likley i know but cant see why
on site we Have 2 DCs, both are GC's DNS and Wins
ad1 i the primary DC
ad2 is secondary
all clients and serves have there dns set as such.
when AD1 goes down
outlook wont open
several database apps wont open
Terminal sevices fails to work
soon as AD1 comes back up all is well again.
in testing the client does use ad2 for dns as it should so bit perplexed.
DNS is AD intergrated..
all servers 2003 ent
pdc emulator is on ad2 aswell which makes it even more curious