Yahoo just had an outage due to a cut underwater cable:
https://help.yahoo.com/kb/mail-for-desktop/SLN25527.html?impressions=trueIt's reported fixed (rather, Yahoo is using a workaround) as of November 24, but I keep getting emails about Yahoo issues every day.
Second, both error AUTH401 and IS6530 come from Yahoo's servers. Those may or may not be related to the above, if you search the web, you'll see that both have been going on for years.
What you can try to do is log into Yahoo web mail, log out, log back in. Then try Aqua again.
Ultimately though, this has to be fixed on Yahoo's side.