'su' error after cvsup to current 5.1

Hi all !
I am having a strange problem after cvsup to current from stable (make world/install world) with 
'su' with all accounts in wheel group  except root, more exactly to say :
8:58{2662}netsaint_at_korn ~>$su
Password:
pam_unix: pam_sm_authenticate: UNIX authentication refused
Sorry

i tried to rebuild openpam and libpam, but pam_unix.so seems to be broken. Where could be the problem ?

Thank you in advance.