Problems with mapw() in GL on Personal Iris

[Klaus Boehm]

I have a problem with the 'mapw()'-Function of the GL of the Personal
IRIS machine.
Problem is, that the function is executed, but the two points in the
3 dimensional wolrd surely do not fit to the mouse position given. In
fact they biuld up a 3D-line, which dosn't really differ from the 3D-
line, which can be build using the eyepoint and the viewpoint of the
'lookat()'-Function. Additionally, the two Points delivered from mapw()
are always the same, they are independent of the mouse position, which,
of course, they should not be.
In my program I only use the perspective()- and the lookat()-Functions.
The viewing object, which has to be passed to the mapw()-Function, gets
the same perspective() and lookat() calls which I also use to render my
data.
The question is, if anybody out there has experience with using mapw().
Maybe there are certain circumstances under which mapw() works properly
or could never work.
It would also be great, if anybody could send a part of a sample Program
to me. I am not able to use the pick()-Function.

Hope to hear anything
Klaus