[SOLVED] Cannot set up dual monitors in XFCE or MATE

I am using Debian 7.6 with MATE. I have an AMD quad-core 64bit and ATI graphics.

I do not want the same image in both monitors. I want the second monitor to expand the first.

This worked fine in Salix 14.1 with MATE - no trouble at all.

I first tried this with XFCE 4.8, could not get it to work. So I installed MATE, like I had with Salix, and it still does not work.

I have two monitors: the first is VGA, the second is DVI.

Whenever I go into monitor preferences, and uncheck "Same Image in all monitors" then click "Apply" I get the error message:

The selected configuration for display could not be applied required virtual size does not fit available size.

I have tried every resolution available. Nothing works.

It is fixed. Not sure how.

I tried to set one of the monitor rotations as "left" and both screens went black, and stayed black.

After a hard reboot, I was able to set up the monitors the way I wanted.