By default, it will be in your app data folder:

C:\Users\{USERNAME}\AppData\Roaming\StrokesPlus.net\StrokesPlus.net.bin

Can you send me your settings file? I don't have an issue opening the Settings window and would like to test it out with your file.

Also, you can reinstall the previous version: https://www.strokesplus.net/files/StrokesPlus.net_Setup_0.2.5.7.exe

And you can execute this script once to disable update checks, so it doesn't ask you to update each time (since you'd be running an older version).

sp_config.DisableUpdateCheck = true;

Of course, that setting is saved, so you'd have to call it again with false to resume update checks.