LDAP BIND Problem with Exchange 2003

Event id 8026
LDAP Bind was unsuccessful on directory for distinguished name ”. Directory returned error: [] .

I have DC and Exchange server ( diffrent machines)
Winwods 2003 Standard Server and Exchange 2003
i get the above error msg at least 5/6 times a day an sometimes the exchange services need restarting
anyone has solution to this please let me know
and how to implement it