D-Command Encoder problem

[subwoof]

I seem to have a rotary encoder that will not go into update mode after the first pass of automation. All other pan encoders work fine, but channel 15 will only write the initial pass of encoder pan automaton, but will not allow me to write any more updates. The amber automation led on that encoder will not go "red" when I touch it from then on. It does not seem to matter what mode of automaton I am in, including "write" mode. It will not allow itself to be updated. It seems to pass the encoder test mode, but will not update after an initial write pass during actual use. This is true on all sessions, even a brand new one.

Any suggestions? Can a single encoder be replaced without sending the whole console somewhere?