Windows Live Mail (WLM) receives POP3 mail on only 2 of my 3 Comcast.net accounts: Error codes 0x800CCC90/0x800CCC92

I am using Windows 7 with Windows Live Essentials. My POP3 email client has been WLM for years; (current version: WLM 2011). It has worked  flawlessly until a few days ago. I have 3 email accounts, all with Comcast.net. I can receive my email from Comcast's web client, but not when I download my messages to WLM. I get the following error message:

Unable to send or receive messages for the STEVEN account. An incorrect password was entered. The next time you send or receive messages, you'll be asked to enter your user name and password for this account.

Server Error: 0x800CCC90
Server Response: -ERR invalid username/password
Server: 'mail.comcast.net'
Windows Live Mail Error ID: 0x800CCC92
Protocol: POP3
Port: 110
Secure(SSL): No

I have checked and re-checked my email and port settings, and they are correct---the same for all 3 accounts. There are no drafts sitting in the outgoing mailbox. I use the latest version of Firefox (v.23) and Avast anti-virus. I have turned off my anti-virus and Windows Firewall, but the problem persists. I've uninstalled and re-installed Live Essentials, but that doesn't help. I'm at my wits end. Please help.