Things to check:
Setup>Midi>Midi Studio, make sure your controller is still listed and still has the proper INPUT PORT assigned.
View>Mix Window Shows>show Instruments. Look at this setting (MIX window across the top) and make sure the input is set for your controller(as configured in the Midi Studio setup page) and make sure the output in this same box is assigned to the VI plugin(I have seen assignments get dropped on occasion)
