[cybmole]

maybe someone who knows could post the location of the relevant registry key for manual cleaning.
I had this bug many versions ago; another fix is to find the calibre installer for that specific old version and re-install then remove it. that is how I dealt with it, way back. I think old calibre versions are archived somewhere not too hard to find.

PS I have used CCleaner reg clean in w10 and survived to tell the tale, but I was checking only for specific fault types ( invalid paths) , not for everything. ( I have a still unsolved issue with adobe reader software not working from inside another app ( truefire music lessons) . it is all good on my other PCs, so I suspect this one has either some left over old adobe stuff or some security rules left over from an old install of cryptoprevent . but I cant find either... I have wiped out adobe both with their own tools and with revo, and rebooted then reinstalled but no fix)