perhaps you have accepted permanently a bad certificate in Thunderbird? Check your preferences -> privacy -> security -> view certificates and delete anything that shouldn't be there.
I believe when Tbird/FF prompt you to 'accept permanently' an SSL cert, it is added into there and can cause conflicts like you are seeing.
I remember getting this error in Firefox, but I don't recall the exact steps to get it, but the resolution was clearing out the 'accepted' certificates. |