User Manager for Domains(NT4.0sp6a)

I can use user manager f/Domain’s on a PDC to see/use other Domain’s (including Domain “A” which I have two way Trust). But from the BDC I get a “Cannot find Domain Controller for this Domain” when I try to choose Domain “A”. Therefore I can not setpermissions to resources on the BDC to other Domains, But can from the PDC.