Writer's cramp. No single treatment strategy is appropriate for every case of writer's cramp. One of the most effective methods is adapting tasks to try to avoid triggering the dystonic movements--this may involve occupational therapy or using assistive/adapted devices.
Something wrong. There is some disorder going on involving the neuro system or muscle system or more likely one of combinations called 'neuromuscular' disorders'. This is actually a complex differential diagnosis, and I would refer you to a good neurologist (such as arielle kurzweil, chief resident neurology, nyu, whose presenting paper in ireland--today is bloom day, celebrating their hero, james joyce-:).