I have a similar problem as this question. I'm trying to learn blender, and am attempting to rig a low poly dog model, but when I rotate one of the legs in pose mode, the opposite side leg follows, but I can't figure out why. I made my rig the parent of my mesh by first selecting my mesh object, then my armature, hotkey Ctrl+P and selecting “With Automatic Weight”. Per the answer to the similar question I mentioned, I followed all the advice there (applying scale and rotation, fixing normals, etc.). The mirror modifier I used to create the mesh has been applied. There is a subdivision modifier and a decimate modifier both on the object (not yet applied), but neither applying nor removing those fixes it. I've moved the armature modifier to the top also, but that doesn't solve it either. In every tutorial I find, it seems they are able to use "With Automatic Weights" with no problems -- what am I missing?