Putting this up there in case anyone else runs into this weird error. Also trying to write the text using all the search terms I used.
The BIOS for my Dell MIni 9 was at A04, and Dell have just released a newer version A05. So I downloaded it onto my machine from their support center and started the flashing process. The update uses Pheonix' WinPhlash program to flash the BIOS.
Actually let's back up. You download an executable, sure, but what it does is to unpack itself in some folder or other and then execute the WinPhlash program. This pops up the main window/dialog for the app but auto-executes it. You don't have to click the Flash Bios button at all. All great until, wham, I got an error dialog stating that the BIOS was not flashable. Exclamation mark. Error -144.
The error dialog said to view the help file for troubleshooting (and there was the button for it in the dialog underneath), but on clicking the OK button for the error dialog, the program just went away. Nice.
So I went to find the folder into which the app had been unpacked (by default,
C:\Windows\Temp\WINPHLASH) and ran the WinPhlash.exe app manually. And then went back and ran it as Administrator, for of course it wouldn't run otherwise. Clicked on the Help button to view the help file. Said help file of course had absolutely no troubleshooting page, let alone a list of error numbers and descriptions. I know, because I viewed every page in the help. Completely useless. Thanks, Phoenix Technologies.
So I googled for a while, varying my search terms, and eventually came across a hint that the error meant that you shouldn't flash while on battery power. You should only flash the BIOS when plugged into a power socket.
And, by gum, it was right. I plugged my fully-charged Mini 9 into a power socket and the flashing process went off without a hitch. So error -144 means "Plug your laptop in to flash the BIOS". The BIOS is flashable, just not on battery power.
Queen - Flash
(from Greatest Hits)