Comment 3 for bug 581900

I'm having the same problem upgrading from Karmic to Lucid using Update Manager. While downloading packages I get an error dialog saying:

"Could not download the upgrades"

"The upgrade is now aborted. Please check your Internet connection or installation media and try again. All files downloaded so far are kept."

"Failed to fetch http://mirrors.us.kernel.org/ubuntu/pool/main/c/compiz/compiz-plugins_0.8.4-0ubuntu15_i386.deb Hash Sum mismatch"

... and a Cancel button.

The compiz-plugins_1%3a0.8.4-0ubuntu15_i386.deb file you mention above does not exist. It seems it hasn't been downloaded, or has been deleted when the hash check fails. Here are the only compiz* files in the directory:

/var/cache/apt/archives/compiz_1%3a0.8.4-0ubuntu15_all.deb
/var/cache/apt/archives/compizconfig-backend-gconf_0.8.4-0ubuntu2_i386.deb
/var/cache/apt/archives/compiz-core_1%3a0.8.4-0ubuntu15_i386.deb
/var/cache/apt/archives/compiz-fusion-plugins-main_0.8.4-0ubuntu3_i386.deb
/var/cache/apt/archives/compiz-gnome_1%3a0.8.4-0ubuntu15_i386.deb

If I retry the update, I get the same error on the same file. It's the only file missing, preventing the update.