When a Skype for Business Online (formerly Lync Online) user tries to sign in to Lync Mobile 2010 on Windows Phone 7, they 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 problem on Windows Phone 7, manually import the missing root certificate chain to the device by sending this file to yourself as an attachment to an email message. To do this, follow these steps:
Download the Baltimore Cyber Trust root certificate chain.
If you're on a mobile device, scan the following tag, and then download the certificate directly to your mobile device:
If you're on a computer, download the root certificate here. Save the file in a location that's easy to access so that you can transfer it to your mobile phone.
If you downloaded the root certificate chain to a computer, the next step is to transfer it to your phone. The easiest way to do that is to send an email message to yourself, and attach the file that contains the root certificate chain. Make sure that you send the message to an email account that has already been added to your Windows Phone 7.
After you transfer the compressed (.zip) file to your Windows Phone 7, open the attachment or compressed (.zip) file to extract the contents. To import the root certificate chain, click each file in the compressed (.zip) file, and in the following order:
After you import the new Baltimore Cyber Trust root certificate chain, restart the Windows Phone 7 device, and try to sign in to Lync Mobile 2010 again.
Lync Mobile 2010 clients on Windows Phone 7.x devices can't sign in to Skype for Business Online or to Lync server because they don't yet trust the newly deployed Baltimore root certificate chain or because they are missing this root certificate chain.
Note This problem may also occur on other devices.
For more information about this change, go to the following Microsoft websites:
Microsoft Knowledge Base
2855339 Skype for Business Online Service SSL certificate changes for client connectivity
The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.