[Fedora-directory-users] Random UID not found problem

Hi, Some of our users get "UID xxxx not found" message when they open a new terminal or run a rsh command, it appears a few times a day and it is mostly just annoying message because users can continue to work as normal, however, sometimes It also causes cron jobs to fail, In system log, it shows, crond(pam_unix)[9225]: could not identify user (from getpwnam(USERNAME)) crond[9225]: User not known to the underlying authentication module We are using Fedora DS 1.0.4, and clients are RHEL 4.5 . This problem started ever since we switched into LDAP three months ago. Thanks