already tried this :-(
root@webserver:~# gpg --keyserver keyserver.ubuntu.com --recv-keys 6DC3D600CDEF74BB
gpg: key 6DC3D600CDEF74BB: "KernelCare <
[email protected]>" not changed
gpg: Total number processed: 1
gpg: unchanged: 1
root@webserver:~# apt-get clean
error still...