When I try to make my object manifold after I do a boolean, this happens:
The weird thing is, it only does this on a few of them, but not all of them.
Near the bottom of the error message it says: "No edges selected". Try selecting the geometry that you want to make manifold, and try the operation again.
I guess I should have added that part in, I tried that several times. After it does the operation, it deselects the geometry.
Ok, so I played around a little bit and I was able to get the error as well. It seems to happen when the addon doesn't like the threshold value. Try changing that to something else...
For the manifold. I got the same error message when I changed that too much.
Really sorry to hear that. Playing around with it in 2.79 I don't get any error messages. I guess the addon is a little broken in 2.80. When I got the error message, I just pressed Esc and continued to play with the manifold threshold. Then again, I just used simple geometry to test... if that still doesn't work for you....guess I'm out of ideas...
I probably could just copy paste to 2.79 if it works there. I'll try it tomorrow.