I also started getting these messages. Thought it may be a corrupt install or issue with my account settings. Remaking the account did not fix, uninstalling/reinstalling Webmail and Yahoo extension did not fix. Actually, the last seems to have broken it more! Now I don't get the "negative vibes" message, but a "cannot connect to server" popup instead.
FWIW the errors it had been throwing were "unable to connect" with error codes 400 and 202 (I believe - the last may have been a 200).
