external editor under windows7

Hi all,
I modified the prefs.lua with:
    prefs.external_editor = "notepad++ D:\\%s"
After pressing Editor button, the message box
    D:\s764 doesn't exist. Create it?
showed up and then notepad started with new,
empty document window. However, after editing,
saving text end exiting the editor, nothing happened
("Create text object" window in Ipe was still empty).
Any help will be appreciated.
Best regards,
Jerzy