[Section1]
Key1=Value
Key2=Value
[Section2]
Key1=Value
Key2=Value
и так далее.

 class IniFile
    {
        [DllImport("KERNEL32.DLL", EntryPoint = "GetPrivateProfileStringW",
          SetLastError = true, CharSet = CharSet.Unicode, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
          private static extern int GetPrivateProfileString(
          string lpSection,
          string lpKey,
          string lpDefault,
          string lpReturnString,  //StringBuilder lpReturnString,
          int nSize,
          string lpFileName);

        [DllImport("KERNEL32.DLL", EntryPoint = "GetPrivateProfileStringW",
          SetLastError = true, CharSet = CharSet.Unicode, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
        private static extern int GetPrivateProfileString(
        string lpSection,
        string lpKey,
        string lpDefault,
        StringBuilder lpReturnString,
        int nSize,
        string lpFileName);

        [DllImport("KERNEL32.DLL", EntryPoint = "WritePrivateProfileStringW",
          SetLastError = true, CharSet = CharSet.Unicode, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
          private static extern int WritePrivateProfileString(
          string lpSection,
          string lpKey,
          string lpValue,
          string lpFileName);

       private string _path = "";
       public string Path
       {
            get
            {
                return _path;
            }
            set
            {
                if (!File.Exists(value))
                    File.WriteAllText(value, "", Encoding.Unicode);
                _path = value;
            }
        }

        public IniFile(string INIPath)
        {
            this.Path = INIPath;
        }

        public void IniWriteValue(string Section, string Key, string Value)
        {
            WritePrivateProfileString(Section, Key, Value, this.Path);
        }

        public string IniReadValue(string Section, string Key)
        {
            const int MAX_CHARS = 1023;
            StringBuilder result = new StringBuilder(MAX_CHARS);
            GetPrivateProfileString(Section, Key, "", result, MAX_CHARS, this.Path);
            return result.ToString();
        }

        public string GetIniFileString(string category, string key, string defaultValue)
        {
           string returnString = new string(' ', 1024);
           GetPrivateProfileString(category, key, defaultValue, returnString, 1024, this.Path);
           return returnString.Split('\0')[0];
        }

        public List<string> GetCategories(string iniFile)
        {
            string returnString = new string(' ', 65536);
            GetPrivateProfileString(null, null, null, returnString, 65536, iniFile);
            List<string> result = new List<string>(returnString.Split('\0'));
            result.RemoveRange(result.Count - 2, 2);
            return result;
        }

        public /*static*/ List<string> GetKeys(string iniFile, string category)
       {
           string returnString = new string(' ', 32768);
           GetPrivateProfileString(category, null, null, returnString, 32768, iniFile);
           List<string> result = new List<string>(returnString.Split('\0'));
           result.RemoveRange(result.Count-2,2);
           return result;
        }

    }

 public List<string> LoadIniFileToStructure(string file)
       {
           List<string> buffer = new List<string>();
           StreamReader sr = new StreamReader(file);
           string strline = "";
           //string ini_record = "";
           string section = "";
           string key = "";
           {
               using (sr)
               {
                   while (!sr.EndOfStream)
                   {
                       strline = sr.ReadLine();
                       //find section
                       if (IsSection(strline))
                       {
                           //if there is a previous record - store it
                           if (!string.IsNullOrEmpty(section))
                           {
                               buffer.Add(section + key);
                               //section = "";
                               key = "";
                           }
                           //record section
                           section = strline + "\r";
                       }
                       else
                       {
                           if (IsValidKey(strline))
                                key += strline + "\r";
                           else
                               key += strline + " is invalid key\r";
                       }
                   }
               }
           }
           return buffer;
       }

List<string> data = LoadIniFileToStructure(ini_file);
data.Sort(); //тут все красиво 
File.WriteAllLines(Globals.IniFilePath, data.ToArray()); //а вот тут эта падла убирает все "\r"