Error in pardiso back substitution

I was simulating a cylinder of copper in the free space, but it gave an error when it was, during the simulation, convergin the erro.
The erro was "Error in pardiso back substitution"
The software was Comsol 3.6
Thanks

If you change the "lambda0" or free space wavelength to a larger value it will get past this error but it then is solving for a different frequency. Also the port area needs to be a ~100 times smaller than the wavelength.