External Display blue screen on old 17" iMac with OS X 10.6.6

Well, after re-imaging one a computer suite of old 17" iMacs (2005/6 model I think), the one set up with the Interactive Whiteboard, when set to mirror displays, went blue on both screens! When I remoted into it, it appeared fine, but still showed the blue screens on both monitor and projector. I tried many different combinations. It appeared when I rebooted the screen would come back to normal and then when I logged in under users which I'd played around with under their settings it went back to showing the blue screen.

One of the problems might have been because the minimum requirement for 10.6 is 1GB RAM and these had 512MB. I thought also that the graphics cards might not be supported in the latest OS.

So I played around a little more, seeing if there was a certain display setting which worked and it appeared there was. I left it for a day and came back, woke it from sleep to find had reverted. I thought it might be the graphics card setting it to sleep which might be the cause of the problem.

I did a few searches and came up with this post which I found in this forum,which proved to work, although as it was an iMac, the energy saving pane looked like this:

I put this to "Never" for both of these. Seemed to fix the problem so far. I shall update this on Tuesday to say if it's still working.

I also had these macs energy saver pane controlled by the Xserver (from workgroup manager). I set workgroup manager preference to "best performance" but it appears this only puts the Display sleep time to "3 hours" (looks like a safety feature). So I had to turn off this preference control and set it manually on this computer.