I have researched this and made the following troubleshooting steps - uninstalled antivirus, checked that server settings are set to security "none", uninstalled and reinstalled Thunderbird and checked with my ISP (webmail is fine). Tried to delete accounts and re-enter them, but I'm unable to delete any of them. Checked saved passwords and there are none. I am unable to download messages but can send them. I'm attaching screen shots of my error console.