IniFile implementation based on the original Windows P/Invoke, grabbed from http://stackoverflow.com/a/14906422/4112816

IniFile.cs

using System.IO;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Text;

internal class IniFile   // revision 11
{
    readonly string _path;
    readonly string _exe = Assembly.GetExecutingAssembly().GetName().Name;

    [DllImport("kernel32", CharSet = CharSet.Unicode)]
    private static extern long WritePrivateProfileString(string section, string key, string value, string filePath);

    [DllImport("kernel32", CharSet = CharSet.Unicode)]
    private static extern int GetPrivateProfileString(string section, string key, string Default, StringBuilder retVal, int size, string filePath);

    public IniFile(string iniPath = null)
    {
        _path = new FileInfo(iniPath ?? _exe + ".ini").FullName;
    }

    public string Read(string key, string section = null)
    {
        var retVal = new StringBuilder(255);
        GetPrivateProfileString(section ?? _exe, key, "", retVal, 255, _path);
        return retVal.ToString();
    }

    public void Write(string key, string value, string section = null) => WritePrivateProfileString(section ?? _exe, key, value, _path);

    public void DeleteKey(string key, string section = null) => Write(key, null, section ?? _exe);

    public void DeleteSection(string section = null) => Write(null, null, section ?? _exe);

    public bool KeyExists(string key, string section = null) => Read(key, section).Length > 0;
}