Well, did you add text to the message you are sending as the error message suggests? Apparently they block link-only messages.

Try using a fresh message and not a draft, old data may have gotten wonky.

Yes, I did type in a few words on the drafts, no help. I have sent links only email before this problem. Also tried a new email, no help. Just now I 'reply to sender' your email and same message.

Okay, at least the straightforward stuff is out of the way.

I found this solution, https://support.mozilla.org/en-US/questions/1062601, and this solution, https://support.mozilla.org/en-US/questions/947605.

It seems some house-cleaning may be in order. The first Solution was to update add-ons and clear cookies(+cache?) for Yahoo. The second was to disable Ghostery (may apply to other privacy-oriented plugins and software).

I did the restart with add ons disabled and thought it worked but upon trying to send another email, it did not work. Did the cookies suggestion and cleared cache and it is working for now. I think I got carried away and cleared everything and now I have to retype my entries on all my sign on pages. But I am happy that I can now send emails.. Thanks.

Great! Thanks for reporting back the results.