SSCE31VSTools-ENU.exe installation problem

When installing SSCE31VSTools-ENU.exe I got an error message: “The upgrade patch cannot be installed by the Windows Installer service because the program to be upgraded may be missing, ….”. How to resolve it? Get your Visual Studio.Net installation disk and fund the vs\wcu\SQLCE\ folder. Install sqlmobile30devtoolsenu.msi first and then install SSCE31VSTools-ENU.exe again.