Now running the released version of KSP (1.2.0.1586, 64bit) Same issue here, unable to use KAC to switch vessels--crashes and generates log file; starts up immediately in the tracking station. No other mods other than KAC. Other than that as long as I use the tracking station or local map to switch vessels it is working normally. Love the work that went into 1.2, great new feel and runs a lot smoother. Just can't imagine why KAC didn't become part of the update. Are the people not using KAC writing things on pencil and paper down to keep track of mission critical maneuvers? or just flying one or two missions at a time?
Great work Trigger, I've been using KAC for years.
Waster