If I had to guess, I would say your models.big is already corrupted. I usually check it by opening it up in Biggui and looking for uncompressed faces. You can attempt to compress it in that program and if it crashes when you try, it is definitely messed up.
I usually treat these in this manner:
1. I find an existing cyberface fsh and collapse it with nFSHTOOL.
2. I copy the new bitmap into the folder created by nFSHTOOL, delete the old bitmap, and rename the new one 0000.BMP.
3. I re-index the fsh.
4. I rename the fsh, ord & orl to whatever number I need.
5. I zip it up and install it with TiT.
If TiT is crashing when you try this method, that would also lead me to believe that your models.big is corrupted.