I'm sorry, I am on XP so I can't help you.
If you changed mouse buttons in control panel, are you sure your settings in StrokeIt fit these new button functions? For example, if you switched left and right button, you will probably want StrokeIt to have the right button for "draw gestures by holding" in Preferences. If that doesn't work, perhaps try a different button in Preferences? I am just offering some generic tips.