I keep getting "oops, you cannot communicate by e-mail till you enable Yahoo e-mail communications .

I recently received a number of answers to my posted question, almost all of which contained something of equal value, so it will be hard to decide to whom to give "best answer". I would like to communicate with the others to thank them personally for their helpful response, but when I go to check a box that supposedly enables the required e-mail communications, it doesn't work. I go back there and find that box is unchecked again. What am I missing?