Lync clients on a Windows Phone 7 device (and possibly other devices) are not able to sign in to Lync Server due to a missing root certificate chain for Baltimore root certificates. Check out this article for the step-by-step solution.

Authors: Moustafa Noureddine, Microsoft Senior Program Manager Lead | Mark Barringer, Microsoft Service Engineer

Published: June 28, 2013

Product version: Lync Online, Windows Phone 7

Lync Mobile clients are unable to sign in to Lync Online, because they do not yet trust the newly deployed Baltimore root certificate chain. Users attempting to log in may receive the following error message:

Can't connect to the server. It might be unavailable. Also please check your network connection, sign-in address, and server addresses.

To resolve this issue on Windows Phone 7 devices, you must manually import the missing root chain to the device by e-mailing it to yourself and opening the attachment.

To resolve the issue, follow these steps:

1. Download the Baltimore Cyber Trust root certificate chain.

a. If you are on a mobile device, scan the following tag and download the certificate directly:

b. If you are on a PC, download the root certificate.  You will later email this file to your phone, so save it in a location that is easily accessible.

2. If you download the root certificate chain to a PC, the next step is to transfer it to your phone. The easiest way to do that is to send an email with the root certificate chain attached. Make sure you send it to an email account that has already been added to your Windows Phone.

3. After transferring the .zip file to your Windows Phone device, open the attachment or .zip file to extract the contents. To import the root certificate chain, click on each of the files in the compressed .zip file in the following order:

a. int1.cer

b. int2.cer

c. root.cer

Figure 1. Correct order of files in the compressed .zip file

After importing the new Baltimore Cyber Trust root certificate chain, restart the Windows Phone device, and attempt to sign in to Lync Mobile 2010 again.

About the Author

Moustafa Noureddine joined Microsoft in 2008 and has worked in the Windows division, Office division, and now the combined Lync and Skype division. Today, he is a Senior Lead Program Manager on the Enterprise Asynchronous Communications team in the Skype Division. This includes Enterprise IM & Presence, Enterprise Federation, Compliance, and Integration with various Office components, such as Exchange and SharePoint. 

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