Exchange 5.5 Site Connector to Exchange 2000

[jdonalds]

We have recently setup a vpn tunnel and domain trusts between two separate networks/domains. One side has an exchange 5.5 server running on NT under a 2000 domain but is not integrated to AD. The other side has an exchange 2000 server on a 2000 domain and is integrated with AD. I'm not sure but I believe I have all the permissions set but I feel this may be the problem. When trying to setup a site connector from 5.5 to 2000 I get the following:

The Microsoft Exchange Server computer does not respond.

Microsoft Exchange Directory
ID no: DS_E_COMMUNICATIONS_PROBLEM

Thanks,
Jeremy