ADMT: "Unable to establish a session with the password export server"

About a month ago, I ran into an issue when using Microsoft's Active Directory Migration Tool (ADMT) between a Windows 2003 and a Windows 2008 R2 domain when using the Password Export Server. The error I received was:

"Unable to establish a session with the password export server. Either the currently logged on user does not have sufficient permissions to call the Password Export Server or the account that the Password Export Server Service is running under does not have sufficient permissions on the target domain controller. Verify that the logged on user is a member of the Administrators group in the source domain and that the Password Export Server Service account can change passwords of user accounts in the target domain."

Well after a few hours of working with Microsoft Support, we figured out the issue was due to PAC Validation and that we needed to make registry change on the source DC running the Password Export Server. 

Here is the registry change:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\Kerberos\Parameters]

"ValidateKdcPacSignature"=dword:00000000