I did what you suggested and gave the movieclip PC_H the AS Linkage name PC_H and now it works, the button now places a copy in the target movieclip, but I have one question: Why?
I have no AS Linkage names for the previous movieclips that work... why would I need to do something different for similar movieclips?
How would anyone know to do that from the cryptic and maddening error messages Flash offers?
Like I said, irrational and inconsistent are words that describe actionscript programming all too often...
Thanks for your help, I appreciate it very much!