scottgus1 wrote:What version of Virtualbox do you have installed, and what version of EP are you downloading?
It's in the thread title : Virtualbox 6.1.30 r148432, extension pack comes from the official download page, so 6.1.30 afaik.
Edit: just tried again and now it installs with no error. What I did since my initial message was to actually boot a win10 VM (worked) and checked its configuration (and got a warning in the status area that config was invalid because of usb settings that relied on the extension pack that had failed to install). Now after redoing the grab extension->install, everything is fine.
So I suspect something didn't properly update when I updated virtualbox from 6.1.x -> 6.1.30, and either starting a VM or editing its config cleaned whatever was causing the extension's installation to fail (or to pretend to fail).