Problem running executable on an R/6000

[Robert Lupton the Good]

I have a largish (30k lines) piece of C that I've run on all sorts
of machines, and am now trying to get up on an R/6000. I compiled
with c89, fiddled a little, and produced an executable. So I tried to
run it:

% file rhl
rhl:          executable (RISC System/6000 V3.1) or object module not stripped
% rhl
Could not load program rhl
rhl is not executable or not in correct XCOFF format
Error was: Exec format error
%

Any ideas? I can run hello_world....

				Robert