I see this thread has been around for a while. Several revisions ago when Map started using the IDX files, It checks all the shape files in the export folder to see if some of the attribute tables have FIELD names that appear in more than one column. There may be other protocols it looks for but that is one reason for CAD not to export to a folder.
If no attributes are being exported, I was told the checkbox for Create Uniqued Field should be checked. The Misc property Closed should also be set to Yes. I have also had cases where I had to create a BOUNDARY or BPOLY because the original closed pline would not export.