Comment 6 for bug 631217

Sebastien, I can't remember what particular update broke it because I had about 200mb of updates when it happened. All I know is that it was working, then one day it wasn't.

Not sure how useful this will be, but in the same set of updates a bug was FIXED that had been annoying me for some time: The GDM now appears only on one monitor while the other is black. Previously, the GDM would be cloned across both monitors and stretched. This could be the same package.

The error "could not save configuration" lends itself to suggesting it might be a permissions problem. If you can tell me what file it's trying to write to, I can investigate further.

As for reproducing, just install the latest version of Maverick and use the stock drivers that come with it - I have an ATI card but as Leon reports, it is also reproducible with an Intel card. Simply connect an external monitor (I'm using HDMI, Leon, are you using VGA or HDMI?) and try to change something in System > Preferences > Monitors.