No, I turned off the "boot" bit of AVG too.
The "BSOD" thing is like the Windows post-BSOD inquisition - same screen colour and fonts,but this is Avast checking stuff. It takes a LONG time to do its check before it lets the machine continue. It gets the "Esc" treatment from impatient me, whereupon the machine continues,
I suspect I ticked a "scan the machine for xxx at startup" box when installing Avast.
Anyway, it's managed to update itself once, and it's done the VRDB thing so progressing OK.