I got on the phone with Yahoo Small Business, and went through the trouble shooting process. ... One of the things about the Yahoo Small Business accounts is Yahoo teamed up with ATT SBC. With that team up, it created a weird log on user name, with two @@ in the user name to use FTP publishing. For example: you need both the [email address]@user-[email address]
The solution, in this case, and recommended by Yahoo Small Business is to
create another FTP User ID independent of the main User ID.
In other words, Yahoo Small Business made a change, it wasn't successfully communicated to their customers, and it took a joint session between one customer and one company representative to realise the oddity
a weird log on user name, with two @@ in the user name
Looking further, we see additional details. Having created a Yahoo FTP User ID, we have to make that User ID usable.
once you've added the new FTP user/password in Small Business, be sure to click the link that says "Enable FTP access" in the "FTP Access Point" column. This gives that new username access to publish on your whole site.
I suspect this is simply one example why Google Custom Domains should be the solution of choice for publishing a blog to a non-BlogSpot URL.
Yahoo Small Business is simply one FTP host. How many others might there be, with similar peccadillo's?