Problem with pressure control on brushes

Hi, since upgrading my Wacom tablet I find the pressure control on the calligraphic brushes very unresponsive - I used to get a gradual increase in line width from 0 - 3 point, for example, but now it just blobs as though I have too much ink in my pen! I tried changing the tip sensitivity in preferences but it hasn'y made a difference. I use these brushes all the time in my illustration, how can I get my fine lines back again?