Script/process/spawner fails silently

Hello.

I am moving an application that uses script/process/spawner in rails
2.0.2 to a new server. After setting up all I can find that needs
setting up on the new box, I go to run script/process/spawner to check
the installation. I get the expected messages, i.e.:

$ script/process/spawner -a 0.0.0.0 -i 3 -p 3000
Checking if something is already running on 0.0.0.0:3000…NO
Starting dispatcher on port: 0.0.0.0:3000
Checking if something is already running on 0.0.0.0:3001…NO
Starting dispatcher on port: 0.0.0.0:3001
Checking if something is already running on 0.0.0.0:3002…NO
Starting dispatcher on port: 0.0.0.0:3002,

but if I check ps aux, I see no such processes, and running the same
script gives the same messages (rather than saying that something is
already running on the ports). I can only conclude that mongrel is
exiting as soon as it is started, but there is no debugging information
I can find to help me track the source of the problem. Is there a way
to get any such information? Even better, has someone encountered and
fixed this problem before?

Thanks for your time.