I can't annotate, my pen and mouse just scrub

For some reason I can’t annotate in RV. If I select a pen then try to draw on the image my pen just scrubs back and forth through the shot.
Same happens with local or shotgrid shots.
I’ve tried turning on the ‘treat tablet as mouse’ setting in prefs, made no difference.
If I uncheck ‘timeline’ then the scrubbing stops, but I still can’t draw…
On a side note, I can’t actually see a ‘timeline’ when it’s selected… I imagine I should.
May just be a bad install?
Dunno, frustrating anyway…