php mapscript draw() error

[James Tuthill]

Hi,

I am just starting out with php mapscript but can't work out what errors 
are causing my maps not to draw().  I started out with simple maps work 
just fine. However, the more complex map data that I purchase don't 
appear to work. These map files renders fine with a normal mapserv.cgi - 
but fails silently at the draw() stage of php mapscript.

This is the simple set of commands that I am using:

    // Create a map object
    $map_object=ms_newMapObj($map_path.$map_filename);

    // Render the map into an image object
    $map_img=$map_object->draw();

    // Save the map to an image file
    $map_img->saveImage($img_path.$img_filename);

The program fails are draw() - but there is no debug output. Can anyone 
tell me how to start debugging this?

Thanks,

James