I'm trying to install Cassandra from package on Ubuntu8.04 based on the info from following page:

http://wiki.apache.org/cassandra/DebianPackaging

I added the two memtioned sources to /etc/apt/sources.list, did an apt-get update, but got the following error

W: GPG error: http://www.apache.org unstable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F758CE318D77295D
W: You may want to run apt-get update to correct these problems

any idea?