Hi, Kent!
I decided to build my armature from the ground up and everything went perfectly until I parented my armature to the mesh. Now, if I attempt to rotate a limb, both sides move (in the same direction) not sure what happened there! Any ideas? Thanks a bunch!!
It sounds like your Mirror modifier is after the armature modifier in the stack (meaning the mirror is visually below the armature in the UI). If that's the case, moving the mirror modifier before the armature (visually above) with the up arrow button in the modifier's box should fix the issue.
Here's the solution: https://cgcookie.com/questions/7191-2-79-symmetrize-instead-of-mirror
Thanks for sharing mmakidoko!