This one is odd. Not sure if I can get you good reproduction steps. But I will talk you through what I did.

  1. Have a .Screen file that is in the Project Explorer, but is not in the .Story.

  2. Click the .Screen file in the Project Explorer and press Ctrl+C to Copy and Ctrl+V to Paste.

  3. Rename the new file to what you want it to be named. X.Screen

  4. Add it to the .Story file.

  5. Double click the .Screen either from the Project Explorer or the .Story file in Storyboard or Screenflow.

  6. A Windows dialog appears stating that windows cannot open the file as it doesn't regonize the filename extension.

Info.

I have about 20 screens, but it doesn't appear to be a screen limit as I have tested it and gone over that.

I am using a workspace in a different place than normal, however this occurs when copying all the files into the normal work place as well.

I have managed to work around the problem by copying and pasting files that are in the .Story but that isn't the problem as I can also copy and paste a different .Screen file which is no longer in the .Story and it works.

I couldn't reproduce this issue. Can you send me your log file using Window > Preferences > WireframeSketcher > Report a Bug? Also make sure all your screen files use ".screen" extension. Note that the extension should be all lowercase as you keep mentioning ".Screen".