File or assembly name 'System, Version=3.9.0.0, Culture=neutra', or one of its dependencies, was not found

Question

I developed a software in Windows Embedded 2013 using Visual Studio 2015 and the .Net 3.9 Compact framework. But when I try to deploy the software, it says:

"File or assembly name 'System, Version=3.9.0.0, Culture=neutra', or one of its dependencies, was not found."

I understand that the problem theoretically is that the framework 3.9 is not installed. But it is, and I already tried to set the system.dll to copy to the deployed system.

This is the code that I'm trying to run:

If instead of

Application.Run(new frmprincipal());

I change it to:

Console.writeline("abcdefg")

it works perfectly.
But I really need some help on this.

using System.Windows.Forms
namespace test
{
    class Program
    {
        static void Main(string[] args)
        {
            Application.Run(new frmprincipal());
        }
    }
}

What can I do?