When trying to launch a .NET 4 application, you get:
System.DllNotFoundException: Unable to load DLL ‘sqlceme35.dll’: The specified module could not be found. (Exception from HRESULT: 0x8007007E)
The Unable to load DLL ‘sqlceme35.dll’ error occurs in .NET 4 applications because the assembly used to compile the sqlceme35 module (System.Data.SqlServerCe), actually references .NET Framework 2.0 in the code.
To fix this, install .NET Framework 2.0 on the PC (Note that you won’t have to do this on Windows 7 because .NET 2 is built in. Also, for some reason Windows 8.1 has the required module, despite not having .NET 2.0 installed).