I recently switched from PC to Mac (Lion OS).  I wanted to stay Mac native so I dowloaded Draftsight and have been quite happy with it for a few weeks.  However, today I opened Sketchup (v 7.1, free) and tried to import a DraftSight dwg file I had been working on.  I got an error window saying:

Error opening AutoCAD import file: No filenameThis does not appear to be a valid AutoCAD DWG or DXF file or the file is write protected

Since I've only been using DraftSight a short time, I assumed this is a DraftSight issue.  To confirm this, I went back to the same Sketchup drawing and tried to import an AutoCAD dwg from before the Mac switchover that I had NOT yet opened in Draftsight - success.  I also tried importing other DraftSight dwgs from the last couple of weks - none of them work.

So either I am somehow write protecting my Draftsight dwg files (I can't find anything on Write Protection in the Help menu) or the Sketchup 7 is not recongnizing my DraftSight files as being "real" dwg files.

Any ideas?  I appreciate any help.