[Users] Not downloading from Gmail

[John Jason Jordan]

I have Claws Mail 3.11.1 (from the repositories) on Xubuntu 14.04, up
to date.

I have set up three accounts, a POP3 for my comcast.net e-mail
account, an IMAP for my university e-mail account (which uses Gmail),
and another POP3 for a regular Gmail account. When I click on Get Mail
Claws places all the mail into my Inbox from the Comcast and university
accounts, but never picks up anything from the regular POP3 Gmail
account. 

I have been using this setup for years and it always worked perfectly
before, but lately I started noticing that I was not getting the mail
for the POP3 Gmail account. Just now I logged in to this account with
Firefox and was stunned to see 384 e-mails in the imbox. This
account only gets half a dozen e-mails a day, so apparently the problem
has been going on for some time.

I looked through the configuration for this account and couldn't see
anything wrong. But when I looked at the log I found this:

[14:25:24] POP3> USER johnjasonj
[14:25:24] POP3< +OK send PASS
[14:25:24] POP3> PASS ********
[14:25:24] POP3< -ERR [AUTH] Web login required:
https://support.google.com/mail/answer/78754 *** error occurred on
authentication *** Authentication failed.

Apparently this is where the problem lies, but I can't figure out from
the above how to fix it. Can someone give me some clues?