Many things can cause a password error, not the least of which is an anti virus program. Nortons in particular have a long standing reputation. Some servers also offer password errors if your settings a incorrect. To diagnose problems with Thunderbird, try one of the following: *Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender. *Restart the operating system in '''[http://en.wikipedia.org/wiki/Safe_mode safe mode with Networking]'''. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: [http://windows.microsoft.com/en-us/windows-8/windows-startup-settings-including-safe-mode Windows 8], [http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-7 Windows 7], [http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-vista Windows Vista], [http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/boot_failsafe.msHi. We noticed that the troubleshooting information was missing from these questions. In order to better inpx?mfr=true" Windows XP], [http://support.apple.com/kb/ht1564 OSX] ; If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates. Should that not identify a cause, please add the troubleshooting information to your post : * [https://support.mozilla.org/kb/use-troubleshooting-information-page-fix-firefox#w_accessing-the-troubleshooting-information-page Finding the Troubleshooting information] *Do you use anti-virus and firewall software? What is the version? *Who is the internet provider? *What is the exact error message? Please post back with this information and any other questions you might have.