Also, in general, whe you want to parent a character to something, use the character's Hip. In your scenario, parent M3's hip to the saddle. The hip is always the master bodypart of a character.

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.