I recently had to export a site and import it to a different server.  Everything worked well using the stsadm export/import command.  EXCEPT when I tested adding a new content type in a Document Library, the document opened in Word 2007, but I got an error saying the Document Panel will not load and I was not able to add in any metadata for this document.

It turns out that I have two lookup columns on the site which contain metadata for a content type and to resolve this problem, I had to delete and recreate these columns, then add them back into the content type.

Luckily I had set these columns up in a parent content type and was able to push down these changes to the other content types inheriting from this parent.