iPhone OS 2.1 beta 4 installed, iPhone Simulator with new firmware?

You should have a newer version. In my case it is 2.1 (5F116). Everytime a new beta is released I completely uninstall my Xcode application including the iPhone Simulator before installing the new one. Maybe that could help.

As mentioned above I would suggest to completely uninstall Xcode. After that you can install the newest version from scratch. To uninstall Xcode you will have to use Terminal. Within the Terminal, type in the following line:

+sudo /Developer/Library/uninstall-devtools --mode=all+

At least that is what works under Mac OS X 10.5.4. The uninstall process may take a while. When it is finished just install the newest version of the SDK. You should then have the iPhone Simulator in version 2.1 (yes, under Settings -> About).

Stupid question: where can I download the beta 4? Can you send me a link?

Same stupid question: Where to get the BETA 4?

As a registered iPhone developer you can download the iPhone OS 2.1 beta 4 and the iPhone SDK for iPhone OS 2.1 beta 4 from the iPhone Dev Center on Apple's Developer Connection.

But i think the one which is there on the apple's site is OS 2.0. Its quite clearly mentioned on their site

Yes, but when you log in, you get access to the beta versions of 2.1.