Error 0xe1000051. Cannot compare password hashes and Error 0x800706ba. The RPC server is unavailable.

We have a Domainpair where the Source AD didn't grant full administrator access. In the Target AD we have full Adminaccess for the Service account.

So we have configured the serviceaccount in source AD based on the manual and use the preinstalled Service Feature.

Installation with AllowAccess.ps1 <SourceDomain> <ServiceUser> at Source DC and AllowAccess.ps1 <targetdomain> <serviceaccount> at Target DC runs without any Problems.

EnablePreinstalledMode.ps1 in a x86 Administrative Powershell cmd runs also without any Problems.

If I try to migrate a Useraccount, i got following Error-Messages:

Error 0xe1000051. Cannot compare password hashes, source user: "xxxxx", target user: "xxxxx"
Error 0x800706ba. The RPC server is unavailable.

Firewall and AV are not installed on Quest Server or DCs. 

Someone any Idea what could cause the problem?