signtool.exe not found

When check the [sign the Xap File] checkbox, build project failed due to

signtool.exe not found.

Follow these steps:

1. Make sure windows SDK is installed: http://msdn.microsoft.com/en-us/windowsserver/bb980924.aspx 

2. Make sure this path is contained in the system environment variable [path] (this path is for .net 4.0/4.5)

C:\Program Files (x86)\Microsoft SDKs\Windows\v8.0A\bin\NETFX 4.0 Tools

And this one:

C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\Bin

3. Make sure the tool signtool.exe is there, if not download one from internet.