Intermittent squid_ldap_auth error:

[Julie Xu]

Hi
 
I have a squid3.1 with redhat 6. and it has errors:
 
squid_ldap_auth: WARNING, could not bind to binddn 'Can't contact LDAP server'
 
I could not find any connection issue, and there is no firewall issue. 
 
Could I have some advice about redhat system itself? If possible some thing may cause ldap authentication problem? 
 
or any idea how to pin-point the problem
 
Any comments will be appreciated
 
Thanks in advance
 
xll