Test connection failed ADsOpenObject(): 0X8007203A

Okay, yesterday I've received message from the customer, saying that some of the update process to Active Directory failed and it causing the virtual user status to update needed. Turn out that the connection test to the Active Directory server is failed, with the error message 'ADsOpenObject(): 0X8007203A', although there's no changes in the Active Directory server. The ping and telnet test work out fine too.
Turn out the problem is in the gateway services. The services run just fine, the status is started. But after we restarted the gateway service, the connection test is working fine, strange. I still don't know what the cause is, maybe there's bug in 6.0sp1 or what I'm not sure. Have to upgrade to version 8.1 fast...