Rhino 4.0 and 32-bit Rhino 5 crash while trying to browse for a .dwg file from the Open, Insert, Import, Save, SaveAs, or Export commands.
Your computer has
AutoCAD 2005, 2006 or 2007 installs a shell extension called AcSignIcon.dll. This shell extension loads into Rhino's File Open dialog box. This shell extension often causes Rhino to crash while browsing for .dwg files.
Disable the AcSignIcon.dll Shell Extension: