Question about μWave's fcmax

When I simulate a combline fiter in μWave
cutoff freqency=20ghz, errors occurred and information displayed as below:

ERROR 1: Internal error in project [Combline.circuit_1]: Error for structure spres_31: critical order is exceeded by 166.66666667%
INFO in project [Combline.circuit_1]: Structure can be analyzed up to fcmax = 12.00000GHz
ERROR 1: Internal error in project [Combline.circuit_1]: *==> Execution Terminated!
ERROR 1: Internal error in project [Combline.circuit_1]: Error in subroutine destroy_qres: unable to (de)allocate memory
Program terminated with an error! ---Error occurred at f=1.800000 GHz [1.point]! Calculation time (0:00:00)

In order to get precise results, how can I modify the "fcmax" ?
Thanks in advance!