I've released an update that gets the Skin Editor to work properly with Paint.NET and GIMP. You only need to download it if you're using either of those to edit images (no other changes are included).
http://www.sonarplus.co.uk/pages/downloads.aspx It's still shown as Beta 1, but it
has been updated. Download it again, and overwrite the older version.
Also, for anyone who has read some of the previous posts on this thread, and seen one or two worrying bug reports (which may have put you off using it), I'm happy to report that the Skin Editor is in the clear. In both cases, the Skin Editor was actually working fine all along, and the bug reports were made in error. It seems the Skin Editor is working very well so far.
Thanks,
Ben