I have 2 different domains that I have linked via IPSec VPN.
I have added DNS Suffix searches to each domain and have created secondary DNS servers in each respective domain.
From Domain1.Local I can ping all machines in Domain2.Local and vice-versa.
From Domain1.Local I can create a trust to Domain2.Local
From Domain2.Local I get the following message "The name you specified is not a valid Windows domain name." When I try and create the trust back to Domain1.Local.
Both are running Windows Server 2003 Domain Functional Level and both are running Windows 2003 Forest Functional Level.