I got the same error message and, for my particular case, found out what the problem was. (Short answer: make sure all model geometry is selected under Edit -> Mechanica Model Setup) Here's a description of my problem:
I had an assembly with two parts. I did the first-time Mechanica Model Setup by selecting the two component surfaces (I'm doing an axisymmetric). Everything ran fine. I then modified the way the components were defined in ProE (Standard Application, not Mechanica). After fixing everything (or so I thought) that broke in Mechanica as a result of my assembly changes, I got that error message. I finally figured out that I had to go back into Edit -> Mechanica Model Setup. Only one of my surfaces was selected. After selecting both surfaces, I got the model to run without error messages!
I later added a third component to my assembly and added forces and contacts in Mechanica. At first, I did not add this new geometry in Mechanica Model Setup. I got the same error message. After adding the new surface in Mechanica Model Setup, it works with no error message.
Hope this helps others. Good luck.
