Geez... this whole thing is becoming a nightmare... the paw is from a pdf (vector) from the mfg. that I projected (direction) to the surface you created earlier. I then trimmed > extruded > exported to *.stp and iserted into an earlier version of my 123D file (pre-paw) Everything worked great up to this point. I then constrained (tangent assembly constraint) the paw to the spot it was located (worked great, bing-bang-boom). If it's any consolation, 123D would not boolean them together either. I thought it was a shortcoming of 123D so I exported (both bodies as constrained) to *.stp and opened in MoI. Here we sit.

;-\

I guess I should start over with tracing the pdf with some new curves...

At least the body imported correctly this time... ;-)