When I try to start debugging my windows phone 8 app in Emulator WVGA 512MB
the following error message is showing
The Windows Phone Emulator wasn\'t
what your describing is usually due to a Firewall of a third party Anti-virus.
If your using Symantec follow this procedure https://stackoverflow.com/a/26326528/4446346
If your using Windows Firewall follow this procedure https://stackoverflow.com/a/27685167/4446346
and If you'r using AVG do the following procedure:
One more thing you must do is go to the "Windows Phone Emulator Internal Switch" and uncheck "AVG network filter driver"
open Network and Sharing Center-->Change Adapter Settings-->Properties
Uncheck "AVG network filter driver"