At a customer we did have the problem that the people search within the Lotus Sametime client was no longer working.
The users did get the message "Required directory or configuration information is missing" and in SAMETIME.LOG you could see the error "Open directory has failed - internal error (0x3)".
The customer was using Lotus Domino as LDAP server. The problem could be solved by setting the LDAP timeout value back to 0 seconds (which is also the default). They set the value to "15" before.
You can change this in the Domino default configuration document under "LDAP -> Timout".
After restarting the LDAP task the people search did work as expected again.