Can't export POLYLINE layer to pdf file

[Jedi Knight]

I have a POLYLINE shapefile. 
In map file if I config "TYPE POLYLINE" it will be error ( Can't run shp2img
utility to export map to image ).
Then I change by "TYPE LINE" then it works. But only when I export from map
to images like PNG,JPEG... When I export map to PDF, this layer not show (
when it does with POINT or POLYGON ).
What should I do to correct. Thanks!