Beam - Plate : Connection

Hello everyone,

I'm trying to custom connections at both sides of a beam. At the bottom side, after creating interfaces the calculation works correctly. But at the top side, even with interfaces I still get the Invalid Connection Error. 

Note that the bottom side is covered by soil which not the case at the top. Also, I thought of working with an embedded beam to control the connection at the top, but I get the error code 20. 

Is there something that I'm doing wrong ? 

Thanks.