In my case, this error occurred because the Exchange SRS service was not running. For some reason it did not start at boot time. I restarted the service and the error went away.
As per Microsoft: "This problem can occur if the target server is down, if it is unreachable due to network problems, or if the Active Directory Connector (ADC) Service Account does not have permissions on the target server". See MSEX2K3DB
for additional information about this event.
If the connection agreement has been moved to a E2k or E2k3 server, make sure that the LDAP port is set to 379 (instead of 389) and that the Site Replication Service is started.
Lightweight Directory Access Protocol (LDAP) allows you to query and manage directory information using a TCP/IP connection. Check network connectivity. Verify the user name, password, and port address are correct, and try again. If the problem persists, verify that the remote Exchange server is configured to support LDAP.