Nintex Forms - Document Set

Hi all,

I'm having issues with creating a form for a document set content type.  I create a new library, add a document set content type (a simple content type that inherits from the document set content type).  In the library, I go into content type settings for the document set and click the Edit Form with Nintex forms link.   I select create classic form.

It comes back with "Error:  Cannot use Nintex forms for content type:  ...."

Using Version 4.3.0.0.

Thanks in advance for any help...

Cheers,

Troy