Comment 5 for bug 1912526

I have to say that it is quite a shame that Canonical does not provide a proper solution for this problem, as it has quite a big impact if you cannot update packages with security fixes anymore.

Anyway, I managed to solve the problem. From an earlier repo installation, I had a key file with the troubling filename "isv:ownCloud:desktop.asc" at "/etc/apt/trusted.gpg.d". After removing that file ("sudo rm /etc/apt/trusted.gpg.d/isv:ownCloud:desktop.asc") I was able to import new keys again.