I’d requested a chkdsk whilst in Safe Mode and it just scheduled it for when I rebooted (albeit not trying to boot into Safe) which is when chkdsk failed to run because of the Ng/VM implementation. The fact that you can’t easily defrag the NgBase snapshot file and it growing in size daily, plus the chkdsk failure scenario was enough for me to take the decision to uninstall Secure Virtual Machine - a feature that I’d not known about until these problems started appearing - a pity I wasn’t given the option to select/deselect this feature during the recent Avast 2015 upgrade.