Cha,

  In general this message means that there is no gain or phase crossover in the
the selected frequency range so the gain margin and phase margin can not be
calculated. If you plot the open loop characteristics, what do you see?
1) Is the amplifier setup properly, that is, is there positive open loop gain?
2) Does the gain/phase crossover occur in the specified frequency range?

                                                                     Best Regards,

                                                                         Sheldon