external program execution error

Hi there, I am having problems with passthru, exec, etc. on Red Hat 8 (w/ PHP 4.2.3; Apache 1.3.27). When I use passthru / exec to execute "pwd" or "ls-al" I have no problems executing & viewing the output. However, when I try and execute a program using the command line e.g "./lee54 < GNOM_FILE_g4Dxx4.args" using passthru, the value "127" is returned. What is this? An error code of some sort? I'm 99.9% sure that the external program itself isn't returning this. All the files are chmodded to 777. I don't know if there are there any configuration directives that I need to set or something..? If anyone has any idea as to what the problem could be, I'd be glad to gear it! Cheers, Lee