Any chance, have you done any upgrades which required messing around with the controls or associated wiring?
You can try reviewing the Model B/TC handlebar installation document and see if it is something that you are comfortable tackling.
There two separate connectors that tie into the clutch control tree; perhaps, one of the connectors became lose or backed out?
I'd start there.. or trace the control cable down and see if the wire harness is damaged anywhere along the length of the cable.
Definitely update the forum with the root cause and fix, once you figure it out.. or as I like to say.. " get errr unfaaa..ked"