I'm using a WPF project in VS 2012 with SQL SC 4.0 .sdf file, but I can't connect to (open) it via neither SQL Server Compact Toolbox nor by double-clicking the file in Solution Explorer (it says "The operation could not be completed"). When I try
to open the file from SQL SC Toolbox it says "The version 4.0 Visual Studio DDEX provider is not installed, cannot add connection". I've installed both the SQL SC 4.0sp1 and and 3.5sp2 db engines,and I've also added a reference to the "System.Data.SqlServerCe.Entity.dll"
(SC 4.0 version) assembly. The file .sdf is ok, I've tried it outside VS. Could anybody please tell me What I'm doing wrong? I'm quite new to this.