Can't add additional email account

I have added multiple email accounts to Thunderbird numerous times. Tonight I added one with no problem. However, I tried to add another account and it would not take. That it, the semi-automatic set up screen failed to add the new account. I rechecked all settings many times and they were perfect. Yet Thunderbird won't let me add the account. As a test I tried to add the account to the Windows 10 built-in email client. It worked flawlessly with the same settings I tried to use with Thunderbird. This is driving me crazy. I really wish Thunderbird had a pure manual email account setup routine. I really don't like the automatic system of adding an account. Any help would be greatly appreciated.