Comment 1 for bug 231171

I'm on Hardy but I just downloaded the flashplugin-nonfree_9.0.124.0ubuntu1~gutsy1_i386.deb package, then downloaded the Flash plugin from the same location that the Gutsy deb gets it from (http://fpdownload.macromedia.com/get/flashplayer/current/install_flash_player_9_linux.tar.gz) and checked that the md5sum matches (using the md5sum given in the Gutsy deb), and it has checked out ok.

Which version of flashplugin-nonfree are you trying to install? Do you have gutsy-updates enabled in Software Sources?