Hyper-V replication across the WAN

I've recently been working on Hyper-V replication across the Internet to give our clients the option of maintaining an offsite copy of their server in our data center. Everything was going smoothly up to a point. I set up a site-to-site VPN connection between them and us, built an Active Directory two way trust between their domain and ours, and then tried to enter their Hyper-V host into our System Center Virtual Machine Manager system.  This is where I ran into a road block.

Workstation Unable to Join Domain

I had a computer that would not join a domain. No matter what I tried, it would come back with "The following error has occurred when trying to join the "abcdefg.com" domain: network path not found."  I tried just about everything I came across while searching on Google:

• Disable Windows Firewall
• Run ipconfig /registerdns
• Run dcdiag on the domain controller
• Verify FSMO roles of the domain controller
• Verify reverse lookup zone in DNS
• Ping domain.com 
• Verify _ldap._tcp.dc._mscds.domain.com in DNS