error/auth/auth ldap noconnect all
The error may be caused by a misconfiguration of the server name or bind dn.
This error can be a tricky one; if you use LDAP for all your authentication, once this error arises you may not be able to log into Moodle to fix it. The entries that need to be checked/changed in the case of this error can be found in the database table mdl_config_plugins for the plugin auth/ldap (for MSSQL2005).
The host_url value in particular should be checked to ensure the domain controllers LDAP are using are correctly set.
Moodle may be trying to bind using an invalid username and password combination. If it used to work but doesn't any more, the password may have expired.