Electrostatic Model to Thermal Losses

Im using the (ES) Electrostatic Solver to compute the E&H-Fields from an Electric Potential using a Hexahedral mesh. This works fine. From there when I click Post Processing -> Thermal Losses I'm getting the error:

*Unable to compute a thermal volume loss distribution for electric losses. Check your material settings, or deactivate the electric losses.*

For all materials including I have defined:
-Thermal Conductivity
-Heat Capacity
-Material Density
-Epsilon

I've tried it with and without electrical conductivities/tangent deltas and get the same error.

Any ideas on what to do or what the workflow should be?