I got this error after installing Visual Studio 2015 CTP 6 with Windows Phone 8.1 emulator. Sometimes  you can get this error if you turned off VTx or AMDv in bios. So, first things to do is: make sure that Virtualization is enabled in bios. Next - turn off Hyper-V. After installing Visual Studio with emulator it automatically turn Hyper-V on. And, apparently, Virtual Box cannot work together with Hyper-V. Run cmd.exe as administrator Execute command dism /online /disable-feature /featurename:Mi...