windows phone 8 - Debug with the emulator -

i trying modify icon in manifest file. when tried debug, error:

the application not launched debugging. ensure target device screen unlocked.  

what have do?

similar issue presented here:

http://blogs.msdn.com/b/wsdevsol/archive/2013/08/17/top-5-commonly-encountered-issues-and-solutions-using-the-windows-phone-8-emulator.aspx