This has happened the last two times I've tried to write a reply. I will be writing along and all of a sudden the screen dims and I get the blue circle thingy. Thunderbird locks up and doesn't come back but the red exit button is available. Of course, I lose all the reply I've written. I've never run into this error before and I've been using Thunderbird for years. I'm running v. 139.0.2 (64-bit) on a win-11 laptop, Firefox in the background but no other programs running. I clear my cache at the beginning of every month, so I did that this morning before starting any programs.