Question

This code reads an array of files and should pass them through to the following class library.

    private void btnConvert_Click(object sender, EventArgs e)
    {
        if (rbtnNetIX.Checked == true)
        {
            string[] files = Directory.GetFiles(txtPath.Text, "*.txt");
            NetEDI.NetIX.Seiko.Seiko.Main(files);

        }

should be referenced by the following code.

public class Seiko
{
    public void Main(string[] args)
    {
        List<FileDefinition.FileDefinition> fileDefs = new List<FileDefinition.FileDefinition>();
        foreach (string fileEntries in args)
        {

            fileDefs.Add(CreateFileDef(fileEntries));
        }

        foreach (var fileDef in fileDefs)
        {
            XmlCreator CreateXmlDefinition = new XmlCreator(fileDef.FileName + ".xml", fileDef);
        }
    }

Answer 1

Look at your Main method declaration:

public void Main(string[] args)

That’s an instance method – you have to call it on an instance of Seiko. But when you try to call it here:

NetEDI.NetIX.Seiko.Seiko.Main(files);

… you’re trying to call it as if it’s a static method.

Given the conventions around Main, I strongly suspect you want to make it a static method.

(As an aside, you should probably revise the difference between static and instance members, and have another look at the error message: see if you can work out why you didn’t figure the problem out yourself, so that next time you run into something similar, you can fix it.)