Changing desktop wallpaper on Windows 7 programmatically

All the programmatic wallpaper changes from previous versions of Windows do not work on either Windows 7 or Vista. I have tried many different ways and many technologies untill i found a way that worked on Windows XP, Windows Vista, and Windows 7.

I created a dll using C#. Here is the C# code for it:

[DllImport("user32.dll", CharSet = CharSet.Auto)]
private static extern Int32 SystemParametersInfo(UInt32 action, UInt32 uParam, String vParam, UInt32 winIni);
private static readonly UInt32 SPI_SETDESKWALLPAPER = 0x14;
private static readonly UInt32 SPIF_UPDATEINIFILE = 0x01;
private static readonly UInt32 SPIF_SENDWININICHANGE = 0x02;

public void SetWallpaper(string path, ref string err)
{
    try
    {
        if (File.Exists(path))
        {
            SystemParametersInfo(SPI_SETDESKWALLPAPER, 3, path, SPIF_UPDATEINIFILE | SPIF_SENDWININICHANGE);
             err = string.Empty;

         }
         else
         {
              throw new Exception("Path '" + path + "' does not exist!");
         }
      }
      catch (Exception ex)
      {
           err = ex.Message;
      }

}

The function above accepts a file path of a wallpaper image as an argument along with a variable passed by reference that will return an error message in case of a failure. An empty string will be returned in case of a success.