Assume that you receive a meeting invitation that was created in a Microsoft Lync Server 2013 environment. When you click the meeting hyperlink in Internet Explorer on a Windows Phone 8 device, the mobile client for Lync Server 2013 does not start. Then, you are prompted to sign in to Lync Web App (LWA).
This issue occurs because the Join Launcher application incorrectly reads the user agent string of the Windows Phone 8 device.
To work around this issue, join the meeting by using the Meeting pane in a Lync 2013 for Windows Phone client.