post the model in you can
we might be able to see what that issue is...
obj is a really simple format...
that said - I don't know why people use SketchUp, it's possibly the worst application you can use if you intend to actually use the models for anything other than conceptual design work...and to have the audacity to charge $495...unreal...
there are a ton of better, free applications, blender has been mentioned, Houdini Apprentice, lots of others...