There is no formal (i.e. official) 64-bit version. I think you can find a third-party 64-bit version, but really, that isn't very likely to matter. Some pundits argue that a 64-bit version might actually be slower.

There are other Windows programs which come in 32 and 64 bit flavours, but in one case, (Irfanview) I choose 32 bit because its add-ons and plugins haven't all been ported to 64-bit. I'm not sure that is a big concern with Thunderbird, as the binary dependencies have been largely eradicated. I'm using a 64-bit version for Linux, but by and large this doesn't seem to affect the compatibility or availability of Thunderbird add-ons. Lightning is the one special case here, it seems, but that doesn't matter if the appropriate version comes bundled with Thunderbird.

What antivrus are you using?

Actually, the opening it in safe-mode thing seems to have fixed it. It was my fault because I thought I had already tried that but I don;t think I had a network attached. You can't start Win10 in safe mode like you used to do it, so I had to google it to do it right )with networking).

But I think we can actually mark this as solved - opening is safe mode WITH NETWORKING makes it a lot faster.

Thanks.

Windows' Safe Mode will have disabled your anti-virus…

So, I guess my AV was stopping some kind of update I needed, or something, because I am back in normal mode and it is working now. What a relief, I have been suffering with this for over a month.

The update and anti-virus might be issues in some ways, but the biggest improvement I get is from Disabling the Auto Compact Feature in Settings / Advanced..

Since I did that, I have absolutely NONE of these errors popping up.

One side effect is I can write e-mails from any of my 5 accounts without any interruptions by this error.