Navigator crashes with ifc

Hi

We are trying to create check models in using navigator. All our disciplines have their own model. When trying to create structural ones, we are also including engineer created ifc models for checkers to check against.

I have done this no problem on a number of models already but on my current one, which does have an ifc model already attached, as soon as I try and reference in some other ifc models, Navigator crashes. 

The ifc models appear to be roughly 50mb in size