Exclamation [Q] Add widget to small app issues...

I'm trying to add widget to the small apps list, when I tap the + sign and choose add my own widget, it tries to load the widget list but before it is done, an error message said "Unfortunately, Small App Widget has stopped."

What should I do? I tried to clear the cache / data, stop the app, reboot the Small App Launcher, but it still doesn't work.

With many thanks.