I spent a day or two trying to get this to work, so hopefully this helps someone searching for this.
The Blackmagic Desktop Video firmware updater failed updating my Blackmagic Intensity Pro card from a very old, unknown firmware version to any version I tried. And I tried pretty much all versions between 9.6 and 10.5.
The error reads: “An error has occurred that has prevented the firmware on your Intensity Pro from being upgraded. Try restarting your computer and upgrading the firmware again”
For me, this forum post had the solution: Set Windows’ performance settings to “High”. In Windows 10, that setting is hidden below a very superfluous drop down menu, I missed it at first. It appears that the energy saving mechanism for the PCI bus kicks in at the wrong moment and the firmware updater cannot write to the card.
Other solutions from the forums included setting the PCI slot in the BIOS to Gen 2 instead of automatic, and gradually updating from an older version, and not making one big version jump from 8.x to 10.5.
Stability on 10.5 isn’t great, there is an occasional BSOD when toggling capture on and off, but it mostly works. Other forum posts suggested that 10.3 appars to be a sweet spot of stability. I may try this and update this post if this helps.