Hi. Welcome to DB.
You can ignore the error. It's happening because the default.set file that comes with the old install is incompatable with 2.43 (bugs were fixed that necessitated this). 2.43 defaults everything internally to something reasonable anyway, so just ignore the error and start the program and change the settings to whatever you want or just use the defaults. When you exit the program, it will save a lastexit.set which will get read in the next time and you will no longer get the error.
If you really want to make the error go away, simply delete the default.set file in your DB settings directory.
Sing out if you have further questions.