You cannot sign in to the Lync Windows Store app for Windows 8 and Windows RT devices

To resolve this issue, check the following items:

• You must be provisioned for Lync Online in Microsoft Office 365. If you already are using Lync desktop or Lync on a mobile device, you should be able to make a connection by using the Lync app.
• The DNS records for Lync autodiscovery must be set up for Lync.
• Your device must have a working Internet connection. To check this, start a web browser, and then open any website that you can expect to be available, such as bing.com. 
• The time and date settings on your device must be accurate. To check this, open a Command Prompt window as an administrator, and then run the following command: 

  w32tm /resync 

  This step is especially important for devices that are not joined to a domain, such as Microsoft Surface or other devices that are running Windows RT. The time that is set on the device must be synchronized with the time that is set on the server.
• Your sign-in credentials must be accurate. In your credentials, make sure that your address, user name, and password are typed correctly. 

If you cannot resolve your issue by following these tips, you may have to obtain help from your local support team or from Microsoft Support to resolve the issue. To do this, follow the steps in the "Use diagnostic logging" section.

Use diagnostic logging

You can use diagnostic logging in Lync to capture information about the issue that you are experiencing. This information can be used by your local support team or by Microsoft Support agents to help you resolve the issue.

To use the logging feature, follow these steps:

1. On the Lync sign-in page, sweep from the right side of the screen to access the Windows 8 charms, tap the Settings charm, and then tap Options. Your screen might resemble the following:
   
   
2. Turn on the Sign-in logs and Diagnostic logs options, and then restart the Lync Windows Store app.
   
   Note Make sure that the app is completely closed. To do this, look for app name in the active applications pane on the left side of the screen.
3. After the app is completely closed, restart the application.
4. Reproduce the issue by performing the same actions that caused the issue to occur.
5. After the issue occurs again, update the logs so that they contain the most recent logging information. To do this, follow these steps:
   1. Sweep from from the right side of the screen to open the Windows 8 charms, tap the Settings charm, and then tap About.
   2. Click Save logs at the bottom of the screen. Your screen might resemble the following:
      
      
6. Switch to the Desktop, open Windows Explorer, and locate the following folder to save the logs: 

   %LocalAppData%\Packages\Microsoft.LyncMX_8wekyb3d8bbwe\LocalState\Tracing