Pacman -Syu fails because of required keys missing from keyring

Hello I tried to run pacman -Syu to update my Arch Linux system. Downloading the (39) packages goes well. But when installing I do get messages like: :: Import PGP key 9B7A287D9A2EC608, "David Runge <dvzrv@archlinux.org>"? [Y/n] error: key "9B7A287D9A2EC608" could not be imported :: Import PGP key 94657AB20F2A092B, "Andreas Radke <andyrtr@archlinux.org>"? [Y/n] error: key "94657AB20F2A092B" could not be imported 12 keys could not be imported and pacman thereafter stops the update. I do have another Arch Linux system which doesn't show these errors. Looks like there is an issue with this system. Is there a way to have these keys imported so that I can update my Arch Linux system ? ~Zerro