This answer was helpful... and I removed 2 duplicate verts from my model based on it. When that alone did not fix it, I also removed the subsurf modifier and was able to generate automatic weights. I had been able to assign envelope weights beforehand... and add this note just in case someone else finds this post when seaching on "blender bone heat weighting failed"...

I removed two duplicate verts from my model and it helped. 

When that alone did not fix it, I also removed the Subdiv Modifier and was able to generate automatic weights. I had been able to assign envelope weights beforehand.