I am using a webMethod and can't figure out how to resolve "Server" in the Directory.GetFiles(Server.MapPath) for accessing files in a folder. Any ideas?

Using the following to access files in a folder on a server, I can't resolve the "Server" part. It wants to change to SQLServer, and it doesn't work.  The code works fine in a normal codebehind page, but trying to use it as a WebMethod won't work.
Any ideas?
[WebMethod()] public static ArrayList populateDropDownList(string UserID, string MediaFilesFolder) { ArrayList ual = new ArrayList(); // URL Array List string[] Files; Files = Directory.GetFiles(Server.MapPath(MediaFilesFolder)); var i = 0; foreach (string fls in Files) { string FileName = Path.GetFileName(fls); string extension = System.IO.Path.GetExtension(FileName); FileName = FileName.Substring(0, FileName.Length - extension.Length); if (!(ual.Contains(FileName))) // Eliminate duplicates { ...