A. A. That was silly :-)

Fortunately this can be fixed with two simple commands which should be run from a command session (cmd.exe)

  1. From the Start menu select Programs and then Command Prompt (or select Run and enter cmd.exe)
  2. Enter the following commands:
    ftype folder=%SystemRoot%\Explorer.exe /idlist,%I,%L
    assoc folder=folder
  3. Close the command session

The first command creates a new file type, folder, and the action associated with it. The second command creates the association between the "extension" and its file type.