FastCgiExternalServer vs. static/dynamic

I’m trying to switch to the “external” fcgi method.

In httpd.conf, this works:
FastCgiServer “/tmp/rubystuff/testapp/public/dispatch.fcgi”
-idle-timeout 20 -processes 4
FastCgiConfig -maxClassProcesses 2 -maxProcesses 2 -minProcesses 1
-processSlack 1

This fails with an error (the public/500.html page is returned):
FastCgiExternalServer “/tmp/rubystuff/testapp/public/dispatch.fcgi”
-idle-timeout 20 -host localhost:19999

For the external, I am also starting
$ cgi-fcgi -start -connect localhost:19999
/tmp/rubystuff/testapp/public/dispatch.fcgi 2

But there are no other changes to the configs.

Frthermore,
$ ps ax | grep fcgi
6749 pts/0 S 0:03 /usr/bin/ruby
/tmp/rubystuff/testapp/public/dispatch.fcgi
6750 pts/0 S 0:03 /usr/bin/ruby
/tmp/rubystuff/testapp/public/dispatch.fcgi
7097 pts/1 S+ 0:00 /usr/bin/vim ./public/dispatch.fcgi
7166 ? S 0:00 /usr/sbin/fcgi- -k start

And,
$ netstat -an | grep 19999
tcp 0 0 127.0.0.1:19999 0.0.0.0:*
LISTEN

Could anyone suggest a possible remedy?

Thanks very much,
Jim