Anyone having Issue with the Dynamesh button not turning on? I seem to have to click it many times to get it to respond. I only had 4 layers of subdivides, I drop to lowest sub D, delete higher. I had to mask off a portion of my mesh, Points I could not smooth out. I Next deleted hidden after inverting mask. Next I choose close holes. Holes become closed and I decide to Dynamesh to even the whole mesh out. I can’t seem to get it to turn on. I click it, it blinks but dose not turn on. Very odd… 
Make sure your mask is cleared. Dynamesh won’t work with masking.
thank! ya that was it! must have been a tiny piece of mask I was not seeing.