Perfect answer. I was previously using the version downloaded off the website and the problem started after I started using the App Store version. Thanks for all the help, definitely wouldn't have figured out it was due to the version I was using.

I've downloaded the model in the link below, opened it in SketchUp and exported it as a DAE file. When I open the Import Furniture window in SH3D, click Choose Model and find the file, the model's file (which clearly has the ".dae" extension) is grayed out as if SH3D is seeing it as an unsupported ...