Last week we wrapped up an assembly of a product we are working on. It was free of any errors in the assembly and in all parts. It was being stored on Dropbox (not sure if that makes a difference). Now I am unable to open up the assembly or parts, SW immediately crashes. I can view the files in SW explorer and move rotate them in the view window, but they wont open in SW

Does anyone have an idea what might be going on that is causing this?

We also have a larger version of this product in its own assembly and it is working fine.