Event ID 40961 -  The Security System could not establish a secured connection with the server ldap/Computername.domain.com. No authentication protocol was available.

Causes, symptoms and resolutions:

DNS issues.

1.  If there is there an Event ID 40960, it is more likely a forward lookup zone issue in DNS. Otherwise, the DNS server has a reverse lookup zone.

2. The client uses Linksys router as DHCP and assign the router IP address as DNS. Creating and using Windows server as DNS server fixes the problem.

3. The DNS server uses the ISP DNS as primary DNS and the internal DNS as alternative DNS. Setup the Windows DNS as primary DNS.

4. If this is multihomed computer, disabled DNS registration on the WAN NIC.

5. If you must use ISP’s DNS, you may need to enable NETBIOS over TCP/IP.

The event only occurs when a specific user logon or a specific machine

1.    Backup the user profile and create a new profile for the user.

2.    Remove the computer account from the domain and re-join it.

3.    If you receive this error after changed the password, make sure you logoff all connections. For example, you may still connect to TS using the old credentials.

Services related issues

1. Make sure the NETLOGON service is running.

2.  Start the Site Server Content Deployment (CRS) service.

3.  Incorrect passwords or user names assigned to the service can be the issue.

4. Make sure the DHCP client service is started on all machines including the computers with static IP addresses, for example Domain Controllers.

You receive this Event every hour or DHCP issues

1. Make sure credentials assigned to the DHCP server to register DNS dynamic updates are valid.
2. Incorrect passwords or user names assigned to the DHCP may cause the problem.
3. Make sure the DHCP client service is started on all machines including the computers with static IP addresses, for example Domain Controllers.

NIC related issues

1. Upgrading the NIC driver.
2. Uninstalling/reinstalling the "client for Microsoft Networks" from the NIC.
3. Reset TCP/IP using netsh command.

Service Patches

Installing the latest SP.