I'm using IE9 on Vista laptop.  I start a new message with recipient, subject, and "attachment" or similar in the body.  Then, when I click on INSERT to attach a file, I get a Windows pop-up error saying "Internet Explorer has stopped working A problem caused the program to stop working correctly. Windows will close the program and notify you if a solution is available."; with a radio button to Close program.

I click the button and Outlook then refreshes back to a blank new message form.

This has happened every time this morning during several attempts, even after a reboot.

I did get an error message at least once stating that Windows Defender had closed the program.  When I looked at my Defender settings, IE was already on the allow list.