So, I received drawings from our MPE consultant. The original format of which is Autodesk Building Systems 2007.
I installed the object enablers recommended: first the ADT2007, then the ABS2007
I appended their files into our Navisworks .nwf file and everything was looking good.
I received an updated model from our consultant and when I tried to reload into the .nwf file, the model (the mechanical drawings .nwc file) was not updated. I tried deleting the .nwc file (from a copy of my .nwf) and reloading it that way, but it only loaded as a .dwg, but the .nwc was updated. However, in the original model, I got the new .nwc to read, but it isn't reading as solids. It's like the object enablers aren't working anymore.