how to debug why apachedbi doesn't work?

[Adam Gotheridge]

env: redhat 6.2, apache, modperl installed from rpm. ApacheDBI-0.87 installed.

If I put either
PerlModule Apache::DBI
PerlModule Apache::AuthDBI
in httpd.conf, apache doesn't start, there are no errors to the screen, and there
is nothing in the apache error log. How can I determine why this is not working?

Thanks