Cant sign in. Please check  your account information and try again. I have installed the lync 2010 android client and it worked fine for 2 days, then I signed out and ever since then I get the error "Cant sign in. Please check  your account information and try again". I can login to the desktop version no problem with the credential no problem. can someone pls help. I have a diagnostic log also, but cant understand it

Hi,

use the connectivity analyser to see if there any problem with the External Web Services. this could be most likely the TMG having problems reverse proxy connections to the Front End server

https://testconnectivity.microsoft.com/

Select the Autodiscover Web Services connectivity test