(NB: There's some background here just by way of introduction. If you encounter this problem and don't want to endure my waffling, check the setting I mention below.)
My Fujitsu laptop currently dual boots Windows and Ubuntu, but it's rare that I boot into Windows. Nonetheless, I had a little time spare last week, I figured I might as well catch up on things everywhere and update the Windows install.
Dropping into that did update Windows, and all well and good. Or so I thought.
On restarting, I noticed there was a Fujitsu prompt that appeared, and was a little unexpected. What I was being asked to install was the very precisely named "Battery Charging Control Update Tool". It seems Fujitsu have had some issues with battery quality, leading to a potential fire risk; this tool is supposed to mitigate that.
It seems that, at least for my model of laptop, the tool was attempting to update the BIOS. And you can see how the tool should work on Fujitsu's Hong Kong site (and that page I could only find on the Hong Kong site for some reason).
In the previous paragraph, I say attempting to update the BIOS, because what happened, after the initial preparation stage occurred with the "Continue to update BIOS?" prompt, was that shortly after I clicked "Yes", I saw a lovely Windows 10 blue screen which I think mentioned tdklib64.sys as the cause.
There's nothing I could find relating to this failed BIOS update and these blue screens — although there were mentions of BIOS update failures and tdklib64.sys relating to other manufacturers machines. Finding nothing struck me as strange: it's a fair bet that you'll find at least one person's already complained loudly somewhere about a problem you've encountered too.
Anyway, I rebooted and tried the update again. Same result. Blue screen.
OK then. Third time lucky, maybe? No. Just the same (reliably) unreliable result.
In a moment of fortunate (and rare) inspiration, I remembered that I'd turned on a relatively new security feature — Memory Integrity — in Windows Defender Security Center as I'd spotted it as a setting I'd not enabled already. Perhaps that was the culprit, especially as no-one else seemed to have encounter this failure yet?
Yes. Yes, it was.
Disabling that again meant the update proceeded without a problem, and then I just re-enabled the Memory Integrity setting once again after the BIOS update completed. If you're having a similar problem, check this setting before attempting to update. Maybe this tip helps you avoid the hour I spent figuring this out.