Sorry, but I don't think the update to it worked 100%, it still takes up to several mins to cast it. Looks like the grid #26, where string is only covers a small area of the spell, hence why it is hard to press it.
To make it work I have to move my cursor to the right side of the screen, and for some reason it then manages to press it when I stop moving it moves to cast the spell. The more to the upper right it is, the more often it succeeds.