Intermittent LDAP Authentication problem

[pwcnash]

Hi,
We have configured secured access to one of our portal that requires LDAP authentication. We are running apache web server on RHEL. Users are authenticated on Nevell eDirectory. The authentication fails intermittently and only a restart of apache webserver fixes the problem.
A review of the error log shows the following message.

auth_LDAP authenticate: user ****** authentication failed; /portal/.../..js ldap_simple_bind_s() to check user credentials failed Server unwilling to perform. referrer [......]

any insight on this and a remedy will be very much helpful. This problem is occuring on our production machine and I have to resolve it ASAP.

Please help.

Thanks,
Naresh