I had similar issue on Qubes 4.0.4…
My disk ran out of space (filled up to 99.9%)…and wouldn’t load any VM’s that were not already open (error msg = qrexec-daemon startup failed)
I freed up space (down to 85%)…BUT still none of my VM’s would boot
Issue persisted after reboot…and now not even my usb-net HVM (using USB wifi adaptor) or even template VM’s would boot (same error as above)…
Next tried to set my usb-net HVM to “run in debug mode” (via qube settings)
Terminal window showed no errors and it booted fine…
closed it, unchecked debug mode…all VM’s now working as prior without issue
not sure how to explain this,
thanks to eveyone! esp developers, u guys make my hero list 