ERROR (SFE-74) Error found in protected block by Virtuoso Spectre during circuit read-in

Hi all,

I am using Version 7.2.0.3007.isr10. And the technology is UMC180nm. 

I am trying to do some montecarlo simulations using both "n_lv_33_mm" and "n_33_mm" transistors. 

In fact, the simulations are performed well when I use only "n_33_mm" transistors. However, when I include "n_lv_33_mm" transistors in the schematics, it shows the following error:

Error found by spectre during circuit read-in.

ERROR (SFE-74) : Error found in protected block by Virtuoso (R) Spectre during circuit read-in.

Now, I have added the all three montecarlo corners and I think the model libraries corresponding to the low vt transistors are included. Not sure if i can post the full names of the model libraries here though. 

 If I don't use one of the MC corners, it will show the error:

ERROR (SFE-23) : "input.scs" M0 is an instance of an undefined model n_lv_33_mm.

Thanks in advance,

Bes