The US is required to sell missiles to Taiwan under the 1979 Taiwan Relations Act, and of course, China has a problem with this. China views the Taiwan issue as an interior problem, which the US should not meddle in.
China-US tensions seem to be increasing, and this upcoming weeks' events may increase them further. Barack Obama will be meeting with the Dalai Lama and Taiwan's President will visit the US.
To be frank, this worries me. The fact that war is possible at any time in the future is something to shudder at, and rising tensions with a rising super power is not something desirable. It is to be hoped that Obama and the Chinese administration find some way to ease this tension. The Taiwan dispute will, as long as Taiwan, China, and the US exist, be a source of disagreement, but it would be nice if we could focus on something other than disagreements. How about, for example, the billion dollars worth of goods the US imports from China every day? There's some good there, right?
There must be some kind of analogy comparing this situation to two toddlers and a teddy bear in a sandbox, but I don't know it.