After a day of pretty solid graft on the DearDiary code (most of which I haven't looked at in a good few months) I believe I have the problem for new users fixed.
However, its a VERY big change and it's not been tested as thoroughly as I would like because of the need to get it online as soon as is possible. Therefore, I have taken a complete snapshot backup of the site as of 20:00 GMT, and taken a database backup as of the same time. I don't anticipate needing it but if you notice something strange with the system, in particular with system messages such as your Index Text or Welcome Message, Entry Headers or Footers etc, then please mail me as soon as you can at;
so that I can look into it as soon as possible.
Fingers and toes crossed, or for those of you in Finland, thumbs up...
Note to users suffering this problem
You will need to login to your diary and click the Customize Button, then choose the messages screen, and edit one of the message files under there. The system will now notice that you do not yet have any files stored there and will create them for you. You can then edit them as normal users would have done before the problem.
You can click here to go to the correct screen in the customizer. You will be prompted for your username and password if you are not already logged in.
Steve