After upgrading to Red Hat 6.1, the page-up key stopped
working in the libc5 based version of Nedit.
After downgrading XFree 3.3.5 to 3.3.1, the problem
(I'm using the libc5 version of Nedit from the ftp.fnal.gov
because the version of glibc/lesstif version of Nedit, as
supplied on PowerTools 6.1, is unstable).
I just retrieved this libc5 version, and tried it with the XFree86 3.3.5 server
from 6.1, and I have no problems. Perhaps you have remapped your keyboard in
some fashion, or are not using the standard Xkb extensions.