Updating FTP password in CP fails

[sabregroup]

Hi:

We upgraded servers from FreeBSD 4.11 to a new server running FreeBSD 6.2.

Everything went reasonably well with the move except that when a user tries to update their ftp password in the control panel the following error occurs:

Error: Unable to update hosting preferences: Unable to create system user: usermng: PAM password change failed: 28, Module is unknown

Anyone have any ideas on what the problem is and how to fix?

Thanks