Import Error: Error reading DXF/DWG tables

I'm trying to open a DWG file.

I select OK to the experimental message box, but get an "Import Error: Error reading DXF/DWG tables" after, and nothing on the page.

Ive updated to 2.2.0 rc4, but still the same message.

Is there a way of diagnosing what is happening.

Thanks!