[itsm] Radius Authentication Issues on Windows Server 2008 R2

Hello I had a windows server 2003 R2 configured as a Radius server for my OTRS::ITSM 3.0.1. That configuration worked like a charm, but now I migrated the Radius server to Windows Server 2008 R2 and I'm not able to autenthicate any more. I already double checked shared secret and that the ip address of my otrs is configured on the new server, I sniffed the traffic with Wireshark and it notice that the radius server rejects the access request immediatley (see attachment). Any ideas on how to work arround this? Regards.