CST-tetrahedral mesh problem

I'm getting this error when i try to create a tetrahedral mesh in CST.
"Volume meshing failed for subdomain "background material": At least one surface edge intersects a surface face. Creating a finer mesh may help"
I increased the mesh to model:65 and background:65. I don't understand how much more finer it needs to be cause it is taking up a lot of time right now.

Can you show your model and maybe identify the area where this error occurs?

What is a preconditioner in tetrahedral mesh?...i didn't find anything helpful in the CST help about it and was getting an error 'preconditioner could not be set'