Wanted to share this in case anyone else is bothered by these errors, I use Scientific Linux 6.1, and my usermin log gets these:
[28/Aug/2011:11:25:28 -0700] Perl module Authen::PAM needed for PAM is not installed : Can't locate Authen/PAM.pm in @INC (@INC contains: /usr/libexec/webmin /usr/local/lib64/perl5 /usr/local/share/perl5 /usr/lib64/perl5/vendor_perl /usr/share/perl5/vendor_perl /usr/lib64/perl5 /usr/share/perl5 .) at (eval 15) line 1. BEGIN failed--compilation aborted at (eval 15) line 1.
So, hating "failed" I went to fix it. The automatic install failed in the perl modules - suggested modules.
The fix. Silly red hat people, they took out the "pam" header files.
yum install pam-devel
then install under "webmin - perl modules - suggested"
All good now :)