3D PDF error - Engineering contents of active model could not be loaded.

Hello, when trying to generate a 3D PDF of a bridge beam I get the error shown in the subject line and the PDF file is blank.  Is there a limit on how many elements that can be included in a 3D PDF?  Here is an image of what I'm trying to produce....

thanks,

Kevin

MS 08.11.09.357

Win 7