First, check your SMTP server settings. It may be as simple as not having specified to use existing password for security. Click to 'account settings', scroll down left side until you see 'Outgoing servers SMTP' and click your smtp server. If if indicates no password, then click the 'edit' button and update the option to use password. That tells Thunderbird to use whatever password may already be stored in Thunderbird. Many email providers let this procedure with no password be used for years, but are now getting more sensitive to security. If you are unsure, please share a screenshot of the SMTP page or otherwise share the contents there.

If that isn't the issue, then you may need to contact your email provider to reset the password.

The above help didn't solve the problem 'BUT may have identified the issue.' When I look at the SMTP server for my email addresses it shows my correct user name but unlike our other two addresses which are in dark print and active -- mine is in a very light print, and inactive and I don't know how to fix it. PLEASE HELP this 85 year old guy. Ticket # 115432

Can you post a screenshot of the SMTP pane for the account? That may help.