[gambit-list] gambit cgi error 11

Hi, I'm trying to use gambit 4.0b22 for CGI but am having a problem. A simple script:

#!/usr/local/Gambit-C/current/bin/gsi-script

(define (main . args) (display "Content-type: text/html\n\nhi\n\n") (force-output (current-output-port)) 0)

But I get a "500 - Internal Server Error" every time I try to hit the page. The web server (lighttpd-1.4.15) tells me the script is exiting with a return value of 11 which the gambit manual doesn't document. The script runs fine from command line. If I just throw:

#!/bin/sh

echo "Content-type: text/html" echo "" echo "hi";

into the file, it works correctly so it doesn't look like a permission/configuration/whatever error with the web server. Any ideas on code 11?