Cannot export since downloading dropbox on computer

Failed to save as /Users/tristancochrane/Dropbox/Mac/Desktop/AA -FOREPLAY GRASSMKT/EDINBURGH HOLES/1.Edinburgh Castle/CASTLE PLAN.skp.

The file writing plug-in failed.

I’m getting this message when I try to export my model from Rhino as an SKP file suddenly. Is it related to Rhino or has Dropbox done something weird to my computer?? thanks

Screenshot 2022-02-10 at 19.45.59

Screenshot 2022-02-10 at 19.45.59

Actually I have isolated the problem to just one layer of the model. any ideas how I can fix that element? What am I looking for?
portcullis V6.1 3dm.3dm (2.5 MB)

Hi Tristan -

Does that model export correctly to a SKP file on, say, the desktop, or some location that isn’t mirrored?