Error in CST rearding meshing

In CST EM studio i get an error which says "some degenerated tetrahedrons exist in subdomain 18 background material. Generating a finer mesh for this region or removing smaller features might help". I have two questions.
1) How do I view the subdomains. And check for the solution to my problem?
2) How to make an adaptive mesh in CST?
thanks in advance

I suggest you :
1. share you file to better guidance.
2.I guess you should apply some change in your structure:i.e tend to the zero the thin of the PEC element.

Did you solve the problem because i have the same one? Tnx.