I try to run a rails app on a lighttpd, but the server does not start because the fastcgi-backend fails to start. This is the error log of lighttpd:

2011-08-02 20:43:15: (log.c.166) server started
2011-08-02 20:43:15: (mod_fastcgi.c.1104) the fastcgi-backend /opt/gemeinschaft/public/dispatch.fcgi failed to start:
2011-08-02 20:43:15: (mod_fastcgi.c.1108) child exited with status 13 /opt/gemeinschaft/public/dispatch.fcgi
2011-08-02 20:43:15: (mod_fastcgi.c.1111) If you're trying to run your app as a FastCGI backend, make sure you're using the FastCGI-enabled version.
If this is PHP on Gentoo, add 'fastcgi' to the USE flags.
2011-08-02 20:43:15: (mod_fastcgi.c.1399) [ERROR]: spawning fcgi failed.
2011-08-02 20:43:15: (server.c.938) Configuration of plugins failed. Going down.

My lighttpd.conf looks like this:

server.modules = (
"mod_access",
"mod_alias",
"mod_compress",
"mod_redirect",
"mod_rewrite",
"mod_fastcgi",
"mod_accesslog",
)
server.errorlog = "/var/log/lighttpd/error.log"
accesslog.filename = "/var/log/lighttpd/access.log"
server.document-root = "/var/www"
server.upload-dirs = ( "/var/cache/lighttpd/uploads" )
server.pid-file = "/var/run/lighttpd.pid"
server.username = "www-data"
server.groupname = "www-data"

index-file.names = (
"index.html",
"index.htm",
)

url.access-deny = ( "~", ".inc", ".htaccess", ".htpasswd" )

static-file.exclude-extensions = ( ".fcgi" )

server.port = 80
include_shell "/usr/share/lighttpd/use-ipv6.pl"

dir-listing.encoding = "utf-8"
server.dir-listing = "disable"

compress.cache-dir = "/var/cache/lighttpd/compress/"
compress.filetype = (
"application/x-javascript",
"text/css",
"text/html",
"text/plain",
)

server.reject-expect-100-with-417 = "disable"


include_shell "/usr/share/lighttpd/create-mime.assign.pl"
include_shell "/usr/share/lighttpd/include-conf-enabled.pl"


$SERVER["socket"] == ":80" {
# "^/((?!(setting|freeswitch)).*)" => "https://%1/$1"
url.rewrite-once = ("^/(setting|freeswitch|manufacturer_snom).*" => "$0",
"^/(.*)" => "/secure/$1")

$HTTP["host"] =~ "(.*)" {
url.redirect = ("^/secure/(.*)" => "https://%1/$1")
}
server.document-root = "/opt/gemeinschaft/public/"
server.error-handler-404 = "/dispatch.fcgi"
fastcgi.server = (
".fcgi" => (
"Gemeinschaft" => (
"socket" => "/tmp/gemeinschaft-fcgi.socket",
"bin-path" => "/opt/gemeinschaft/public/dispatch.fcgi",
"min-procs" => 1,
"max-procs" => 2,
)
)
)


}

$SERVER["socket"] == ":443" {
ssl.engine = "enable"
ssl.pemfile = "/etc/ssl/amooma/server.pem"

server.document-root = "/opt/gemeinschaft/public/"
server.error-handler-404 = "/dispatch.fcgi"
fastcgi.server = (
".fcgi" => (
"Gemeinschaft" => (
"socket" => "/tmp/gemeinschaft-fcgi.socket",
"bin-path" => "/opt/gemeinschaft/public/dispatch.fcgi",
"min-procs" => 1,
"max-procs" => 2
)
)
)
#fastcgi.debug = 1
}



running the dispatch.fcgi as ruby script like this: ruby1.9.1 /path/to/dispatch.fcgi produces no error.
when there is no bin-path entry in lighttpd.conf the server starts. But whenever i add

"bin-path" => /some/path/dispatch.fcgi
this error occurs again.
Any hint would be appreciated.