I think I know the problem - when we updated to use better methods for handling colour, it opened up the possibility of handling opacity as None (allowing e.g. different opacities for the fill and outline of a shape), but I missed a call in MovieStim to opacity which doesn’t like None. If you change opacity for your movie stim to be 1 it should fix this error! I’ll also put in a bug fix for the next release to handle None properly.