6.06 to 8.04: error using gksu "update-manager -d"

[jwbat]

Followed the directions on how to upgrade from 6.06 to 8.04 by using:

gksu "update-manager -d"

Then clicking on check for updates.

Error message from upgrade attempt:
http://packages.freecontrib.org/plf/dists/dapper/Release.gpg: Could not connect to packages.freecontrib.org:80 (34.52.53.34), connection timed out

Then another message:
W: GPG error: http://easyubuntu.cafuego.net main Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 580E2519969F3F57

How do i fix/get around these probs?

Much thanks,
JWB

[Pumalite]

Before attempting to upgrade; remove all third parties from your /etc/apt/sources.list