I have put a mecenery camp to buy neutral units on my map, but when I got there with a hero and select "purchase unit" , nothing happens. I have D3 resurrection 1.04

Is that a (known) bug?

Get the latest patch. 1.06.something. The game's really buggy in the latest patch. I'm surprised 1.04 even loads.

1.06 is for Renaissance, I am speaking about Resurrection. Another time I played the map with the mecenary camp, I was able to buy units that time.