i am testing my few LDAP servers by using an LDAP User Experience Monitor and periodically it shows an announce "unknown". I am doing a parallel testing with a command ldapsearch from my computer and get a correct answer. I checked the network and everything is working right.

I check in the same time four LDAP servers and all of them get a problem at the same time.
what does it mean "unknown" in this situation?
what else do I need to check?