LegB Reason: Transport Error on SIP TCP Call

Hi,
we have a strange problem, as soon as a gateway registers “transport=TCP” or I configure Gateway/Signaling/Transport Protocol: TCP" I get LegB Reason “Transport Error” and there is no INVITE to the registered Gateway.
As soon as I change it to UDP everything works, did I configure something wrong? SEMS is listening on 5060 TCP.

LegB Reason “Transport Error” means SEMS can’t establish TCP connection to remote gw