error for mixer in simulink

hi

i have attached the mixer circuit
the input frequency is 2 GHz and local oscillator frequency is 125 MHz
i am downconverting this to get a intermediate frequency of 1.875 GHz
the error message is as follows\

Error using ==> rfckt.mixer.convertfreq
Mixer output frequency is negative. Check FLO of MIXER and the simulation frequency

i have attached the .mdl file
could anybody help me out
thnx