Problem about publishing web feature service when working on Bentley Geoweb Publisher

     Hi all,
     I am working on Bentley Geoweb Publisher and I have got a problem about publishing web feature service.
     I tried to create a web feature service from a dgn xfm data layer, everything seem was ok but when I tested the WFS link with Bentley Map there was nothing to be showed, the notify information is "WFS Service encountered the following issue: Unable to describe feature type "VNM"."
     This problem is only happen on dgn xfm data (that mean It is ok with other data types, example: spatial data...)
     Could anyone please to help me explain why is it and how to fix this proplem. Thank you so much!