Error: "Device has no room for update"

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I have to admit I’ve messed around with the versions of debian libcc and other packages and I’m trying to revert to the standard firmware 05.04.00-342 by manual updating from the web interface.
Could this message be in error, really meaning that you can’t upgrade with the same version as installed?
Where does it need more room? I have got the root filesystem down to 35% usage, better than it was before I messed around, yet I still get this message. the 2TB DataVolume filesystem is 66% full, /run is 11%, /run/lock 1%, /tmp 9% and /var/log 4%.