pba mesher cannot handle bodies

I am designing a probe-fed hollow dielectric resonator antenna with a metallized cavity (using zero thickness for the PEC) in CST 2006. The transient solver warns that the "PBA mesher cannot handle sheet bodies. They will be ignored in the simulation. Try to enable PBA acceleration".

However, the S11 appears to be just slightly off resonance (from 2.446 GHz to 2.434 GHz) compared to the non-metallized cavity. Can I assume that the metallization had no effect?

When I assign 35 micrometers for the metal thickness, the antenna becomes completely mismatched.

Is it a new feature that PEC could be treated as 0 thickness, for i'm still using version 5.0.
BTW, i suppose your very little offset of the resonant frequency could safely be adopted.