Exception: Failed to build Visual Studio project using arguments 'C:\Program Files (x86)\MSBuild\14.0\Bin\MSBuild.exe compile error on windows phone 8.1 platform

Hi everybody, I have been working on a game and everything was going okay! up until now I was testing it on android devices and today I tried on windows phone 8.1 and I get this mind killing error that I can't figure out. I looked the internet and there was no clear answer, here is the description:

Exception: Failed to build Visual Studio project using arguments 'C:\Program Files (x86)\MSBuild\14.0\Bin\MSBuild.exe "C:\Users\GRGS\Documents\UnityProjects\Falling Monkey\WinBuild\Falling Monkey.sln" /nologo /maxcpucount /p:Configuration=Master /p:Platform=ARM /p:SolutionDir="C:\\Users\\GRGS\\Documents\\UnityProjects\\Falling Monkey\\WinBuild\\" /t:Build /clp:Verbosity=minimal'. Output: UnityInstallationDir "C:\Program Files\Unity\Editor". UnityWSAPlayerDir "C:\Program Files\Unity\Editor\Data\PlaybackEngines\MetroSupport". UnityProjectDir "C:\Users\GRGS\Documents\UnityProjects\Falling Monkey". Copying unprocessed assemblies... Running AssemblyConverter... AssemblyConverter done. Falling Monkey -> C:\Users\GRGS\Documents\UnityProjects\Falling Monkey\WinBuild\Falling Monkey\bin\ARM\Master\Falling Monkey.exe C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v14.0\AppxPackage\Microsoft.AppXPackage.Targets(880,5): error APPX1639: File 'MakePri.exe' not found. See http://go.microsoft.com/fwlink/?prd=12560&pver=1.0&plcid=0x409&ar=MSDN&sar=PlatformMultiTargeting&o1=WindowsPhoneApp&o2=8.1 for more information. [C:\Users\GRGS\Documents\UnityProjects\Falling Monkey\WinBuild\Falling Monkey\Falling Monkey.csproj]

ApplicationLauncherImpl.RunMSBuild (System.String args) (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/ApplicationLauncher.cs:294) ApplicationLauncherImpl.Build () (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/ApplicationLauncher.cs:179) ApplicationLauncher.BuildAndRun (BuildLaunchPlayerArgs args, WSASDK wsaSDK) (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/ApplicationLauncher.cs:56) ApplicationLauncher.BuildAndRun (BuildLaunchPlayerArgs args) (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/ApplicationLauncher.cs:46) UnityEditor.Metro.BuildPostprocessor.LaunchPlayer (BuildLaunchPlayerArgs args) (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/ExtensionModule.cs:95) UnityEditor.PostprocessBuildPlayer.Launch (BuildTarget target, System.String path, System.String productName, BuildOptions options) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs:282) UnityEditor.HostView:OnGUI()

Can anyone help me please, thank you in advance.