Had a note from Yahoo that included, in part, the following…
My apologies for the issue you’ve been having with updating WordPress.
Our engineers are working on the situation, and we’re doing all that we can to get it cleared up as quickly as possible. Please watch our blog page at status.smallbusiness.yahoo.com for updates and for our notice of when this issue is resolved.
At least they have admitted that it seems to be on their end now.
Getting this exact error on a site hosted on Yahoo today (15 SEP 2015).
Trying to upgrade from 4.3 to 4.3.1 and no problems with past updates.
No help from Yahoo…”Our systems are 100% up to date. This error is on the WordPress site.”
Any ideas?