Executing System calls under Apache

Our Rails App executes a system call:
system(“app/bin/fitsfetch.sh”, url, dir, item, status_file)

It’s a simple bash script to download a URL and move it to
a new directory while changing the filename (also reporting
a status from a simple status file).

It works fine under Webrick, but fails when we run under
Apache2. I’m guessing it has something to do with the
permissions or some other Apache2 security setting. I’m
not an Apache2 expert. We’ve tried the obvious things
(permissions/ownership/group of the script, ditto on
the directory, etc). But no luck.

Has anyone been able to call shell scripts via Ruby when
running a Rails app under Apache?