Let me help you with this.
The problem you are having is very strange because I have not been able to replicate the problem but there are some steps and information I would like to check from your system configuration.
As first step, I would like you to uninstall the current driver and install the latest for your system. Here you can download the latest driver:
If you find problems during the installation please try the manual driver installation steps mentioned at this link:
Besides this step, I recommend you updating the BIOS in your system and testing different cable for the connection you have.
If you are still having problems please attach here your dxdiag report and your graphics report.
How to get it?
Dxdiag Report: Type dxdiag in Start Menu> open> Save> Copy/Paste here.
Graphics Report: Right click on desktop> Graphics Properties> Options> Drop Down Menu> Information Center> Save> Open .txt file created> Copy/Paste here.
I solved the Problem. After uninstall and reinstall of the driver > same problem. Then I changed the view from "clone" to "only projector" and now I can choose 1280x1024. I have not registered this possibility before.
Thanks for your help.
It is good to know it is working now!