Sorting filenames...please help!

Here is another possible solution:

static void Main(string[] args) {
    string path = <yourFilePath>;
    string pattern = "(?<=.{10})\\w{4}(?=.*)";

    var result = File.ReadLines(path).OrderBy(x => Regex.Match(x, pattern).Value);

    foreach (var item in result) {
        Console.WriteLine(item);
    }

    Console.ReadKey();
}

wizend