How to get rid of External Account Settings message pop up?

[Luckytrail983]

I continually get the following message:

We're sorry, but it looks like there might be something wrong with the settings of the external account . Please check your [account address] in Mail Options and try again.

Have tried deleting this external account from yahoo, but when I try I get an invalid request error message. And it's an obnoxious circle. Pop-up about the external account every time I open a mail message, try to delete the external account, get the error message.

Any suggestions? I'm thinking of just dropping my yahoo mail over this because I can't find any answers to this problem and it's so obnoxious to work around.