Looks like this could be related to: https://bugzilla.redhat.com/show_bug.cgi?id=668196
I tried this on my own Radeon HD 4870 running on Ubuntu 11.10. I have two of the same monitors Samsung 204B. One cable is DVI and the other is DVI->VGA adapter, and VGA cable into the monitor. After plugging this in, I launched the gnome Displays settings and was able to apply the new settings and get this setup to work. ** Bug watch added: Red Hat Bugzilla #668196 https://bugzilla.redhat.com/show_bug.cgi?id=668196 -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to xserver-xorg-video-ati in Ubuntu. https://bugs.launchpad.net/bugs/914437 Title: Second display not recognized anymore; "EDID checksum is invalid" To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-ati/+bug/914437/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp