Right! I have further news.
1) Shutting down ZoneAlarm, virus scanners, etc made no difference. Notepad still opened up with the error. Uninstalling and reinstalling MsgPlus similarly made no difference.
2) Changing the LogViewerProgram entry to something like "wordpad "%s"" meant that the logs reverted to "Can't open the decrypted file!" error.
3) But some success! After following your advice Cookie, I had a look in my Temp folder. There was indeed a "blah@blah.com {decrypted].txt" file in there, which opened with no problems at all. When I OK'd the error in the original Notepad window, the file was then removed.
So, the logs are there and are accessible.
But at the moment, I can't seem to find a way for them to open in Notepad first time, or why the error is occurring. My system event viewer doesn't show any Notepad errors in it. So if we can work out this last part of the conundrum, my life will be complete
