[Exim] question on wrapper, built in mailman

I am using mailman with exim. I have create a mailing test call
"testsystem". After sending mail to testsystem, I got an error message
saying "Child process of list_transport transport returned 69 (Could mean
service or program unavailable) from command:
/usr/local/mailman/bin/mail/wrapper.
In order to debug the problem, I ran the wrapper as "wrapper post
testsystem" and I got nothing.
My question here is that what kind of output I should expect from "wrapper
post testsystem"?

thank you for your help

tao wu