Finfet Stacked CMOS oppoint problem

Hi All,

I'm trying to use "Measuring Stacked-FET Parameters" function of SPECTRE16, in order to find oppoint, such as gm, gds.. for stacked Finfet. I have done all settings specified in spectre user manual, and the results shows that except for 'vth' all other params seem to have been correct simulated. But the value for 'vth' is 'nan'.

this is warning for "vth":

Actually I cannot find a 'ivth' param in mosfet models.. How can I solve this problem?