Please post a screenshot of the error. https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem

Hi, I keep getting this same message each time I try to get messages from my Hotmail account manually. It is set up as an IMAP account but it no longer syncs automatically in Thunderbird. This started happening on June 16 when both Windows 10 and AVAST installed an update. Thanks for any real solution. Robert

Hi, It’s me again. I have solved this problem. All I had to do was to start Thunderbird with Administrative Privileges. I am no longer getting Security Exception messages.