I was having similar but odd problems with postfix related to this. I am using SuSE 9.2 and followed the perfect setup instructions. I would get my mail when I opened the client and the web interface worked fine. But if I would hit send/recieve in my client I would get errors.
My mail log shows the exact same errors as yours, but chainging from pam to shadow did not work for me.
I noticed FAM was not loaded so I:
chckconfig --add fam
and viola no more errors!