can´t connect using dll from windows service

Question

I have a windows form application which is working fine. I created now a windows service with FileSystemWatcher, it went ok.But when I copied the code from the windows form I had before it doesn´t work. (It is working on the windows form)Is there anything I need to take care working with windows services?.The application (windows forms) is to receive a file, make some operations with that information and then using an dll, comms with a scale.

      [DllImport("mydll.dll")]
        public static extern int OPENETHNET();

    [DllImport("mydll.dll")]
    public static extern int ETHWRITE(string in1);

    [DllImport("mydll.dll")]
    public static extern int ETHREAD(StringBuilder in2);

    [DllImport("mydll.dll")]
    public static extern int CLOSEETHNET();  

and then I use it like this:

        string inputStatus = "050";
        StringBuilder resultStatus = new StringBuilder(1024);


        openRest = OPENETHNET();

        if (ETHWRITE(inputStatus) == 1)
        {
            ETHREAD(resultStatus);
        }
        CLOSEETHNET();

It doesn´t even opens the conection..
I tried to change the account to LocalService and the other options but, still the same.. Any ideias?

EDIT: I saw the post Call to native DLL fails from a .NET Windows service ANd It seems to be the same problem
I tried the other solutions but it didn´t worked So I´ll try the last option, that it will be to to "wrap the dll in a web service that will run on start up and then call through to that web service from the web service."
Can anyone explain me how to do that?

Answer 1

After a lot of tests I realised that problem was in the dll file, so I drop the windows services and implement a winform ( where I know that the dll file works) and use the winform like a service, I now this solution is not the best one but, well is working..