The motif libraries were missing. This became a blocking problem when I launched the forms at client side. Frm-92050 was the very message we've got when launching a form.
Look for the missing libraries for the forms server:
ldd f60webmx | grep 'not found'
=> libXm.so.2 not found
Installing the motif libraries from the RH9 distributie. Since this version was too high, I created a symbolic link from the higer libXm to the lower one.