Home > OCS 2007 / Lync 2010 > OCS 2007 R2: CWA Error code: 0-0-18401-0-0

OCS 2007 R2: CWA Error code: 0-0-18401-0-0

Recently I was troubleshooting the following error on the Client Web Access Server:

A problem occurred and the session was ended. Please sign in again. If the problem persists, contact your system administrator.(Error code: 0-0-18401-0-0)

I couldn’t find a lot of info about this error on the Internet but I found that this error was probably related to Certificates.
After a short time I found that the MTLS certificate was not signed anymore in the  Web Access Console, so I re-assigned my Certificate and everything was working fine again. This was quite easy to solve…

There are three places to check the Certificates on the CWA server:

  1. The MTLS Certificate of the CWA server itself in the CWA console (Click on the server name -> properties)
  2. The SSL Certificate in the CWA console (Click on “Communicator Web Access -> properties -> connectivity)
  3. The SSL Certificate in IIS (Communicator Web Access -> properties -> Directory security -> view certificate)

You can use one Certificate that supports MTLS and SSL or you use 2 separate certificates, one for SSL and one for MTLS communication between the CWA and the front-end server. An other thing I figured out is that it’s not possible to request a new certificate on the CWA server even if you have installed the Administrative tools. You need to request a new certificate in the Administrative tools on the front-end server. Click on a poolserver in your pool and right click it and select certificates to open the certificates console.

More info: http://technet.microsoft.com/en-us/library/dd425345(office.13).aspx

Categories: OCS 2007 / Lync 2010
  1. Brandon
    January 25, 2011 at 7:19 pm

    I too had this same error and verified it was certificate based on SipStack trace error of “The connection was closed before TLS negotiation completed. Did the remote peer accept our certificate?”. I then followed this article to check all certs and they all “looked” good, but the MTLS cert showed info for a cert that no longer existed in Personal Certificate store. We then reselected the same cert (with new expiration date) and restarted IIS and internal/external CWA and it fixed problem. We believe what happened was the cert auto-renewed and was stuck in memory and continued working until we rebooted CWA server. So, when someone is troubleshooting this – click to select cert and verify there is really a cert in there that matches info that the GUI says.

  2. Joris
    January 25, 2011 at 7:28 pm

    Thanks for your input Brandon, this info is useful for other persons with the same problem.

  3. Nate
    August 19, 2014 at 6:05 pm

    This article got us back up and running. Thanks.

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