The Lync app (the one you get from the Microsoft Store in Windows 8) just stalls (the wait 'circle' just endlessly circles) while trying to sign in with my Office 365 account.  It doesn't time out or provide an error message.  This happens on both my Surface RT and Surface Pro.  It happened on both devices when I had Windows 8, and continues to happen after upgrading both devices to Windows 8.1.  I'd like to point out that on the Surface Pro, I also have Lync 2013 installed as part of Office 2013 Professional Plus, and Lync 2013 never has a problem signing in.  I can sign in successfully with Lync 2013, then immediately try to sign in with the Lync app and experience the stalling login on the Lync app.

Following the app's troubleshooting tips (linked from the login page), I've tried removing my log in credentials, closing the app and restarting it, and even restarting the Surface.  None of these work.  The only thing that works is to uninstall the Lync app, then re-install, launch, configure, and login to it.  However the Lync app will only continue to work for 1-2 days and eventually the stalled login issue returns.

This has been going on since I first started using Lync in September 2013.  I've had to re-install it several times on the Surface RT.

I can't find anything in event viewer to help with this.  I've read about ensuring that the time is properly sync'd and can confirm the time is set properly.  Again Lync 2013 works on the Pro even when the Lync app won't.

I tried to do a clean reboot following these steps at KB 929135.  However there aren't any non-Microsoft services for me to disable, and there are no start up items to disable.

As I mentioned I updated my Surface devices to 8.1, but I even went to the trouble of completely refreshing them (complete re-install).  They are on the latest firmware, OS, and patch level.

Given that Lync 2013 works fine on the Surface Pro, I suspect the problem is with the Lync app itself, not with the device, Windows, or the Lync service.

• Edited by Steve SOS 7 hours 51 minutes ago Corrected grammer in one paragraph