Hello storkman14
I had the exaxt issue you described. Normally I use my MacBookAir for lectures at university using the lecture theater projector and had not any problems.
However, yesterday, I was working with an NPO and used their prohector and only the Mountain Lion "solar screen saver" wallpaper appeared. But, like you, when I actually started the PowerPoint Presentation slide show, it showed up on the proejctor.
Since I have to give a very important presentation and workshop on Sunday, I contacted Apple Care Support here in Japan to find out what the issue is. I was transferred to a top enginner who quickly knew how to troubleshoot. This solution does not requre getting new software or an official Apple VGA adapter.
Basically, Mountain Lion remembers the mirror setting for every different VGA projector you use. Most projectors have the same the settings, so normally there is no need to have Mountain Lion remember a setting on a different computer. However, depending on the projector, Mountain Lion sees the projector as a new projector. In this case, the mirroring default is no checked and only the solar screen saver appears. Fortunately, the troubleshooting in very simple.
Following these steps:
1. Connect the Mac and VGA adapter to the projector when the projector is on.
2. Go to System Preferences > Displays.
3. Since the computer is connected to the projector, an extra tab between "Display" and "Color" will appear. (Sorry I cannot remember the name of the middle tab as I don't have projector to connect to at the moment.) When the computer is not connected to a projector only the two "Display" and "Color" tabs appear.
4. Click the middle tab and near the bottom of the tab window you will see a check box to enable mirroring. If it is a projector that Mountain Lion doesn't know about yet, it will be uncheked by default.
5. Once the mirroring check box is checked, close System Preferences, and mirroring should now work. If not take the adapter out and re-insert it. If that doesn't work, reboot your computer.
Following these steps should have the projector mirroring your desktop on the projector as normal and since Mountain Lion remembers the setting to be for mirroring for the new projector, it will automatically mirror the desktop next time you connect to this same projector without having to do the above.
I can confirm this works, as I went to university today and used the same projector in the lecture theater I normally do. When I connected the Mac to this projector, the computer switched to mirroring mode without me having to do anything.
Then I tried a different portable projector and the problem you described occurred. I followed the steps above and mirroring was enabled. Then, just to make sure this had not messed up the settings for projector I normally use, I went back to the lecture room, connected the projector and it went into mirror mode without me having to do anything. So Mountain Lion remembers each projector you set mirroring for.
I hope this information helps.
Since, this thread shows many people have the same problem, I asked support to create a new knowledge document about setting up mirroring for new VGA projectors. The request is being forwarded on to the powers to be.
If you and others reading this have the same issue, and follow the steps above, could you kindly post a reply to this comment. Apple communities in Japan is not very active. And top support told me that they monitor the discussions and if there many people having the same issue, they get their engineers working on it. I want to contact support again and provide them with a link to your replys so that the engineers on the Japan side can convince their bosses to write a knowledge based note which is made available in all languages.
Thanks! 🙂
Darren McDonald
Japan