Question: I have an existing project that I was working on, and I recently decided to update my iPhone SDK and updated to the latest 3.0 SDK.

I update my SDK and go to open my existing project. Sure enough, there are some problems including some certificate problems and so on. Anyway, google and I were able to solve most of them, but I haven't had any luck on what I hope to be the last of my problems.

When running my program in the simulator, I now get

> 
> dyld: Library not loaded:
>  /System/Library/Frameworks/UIKit.framework/UIKit
>  Referenced from:
>  /Developer/iGameLib/iGameLib/build/Debug-iphonesimulator/iGameLib.app/iGameLib Reason: image not found
> 
> 
> 

Now, I discovered the UIKit has moved to 

> 
> /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.0sdk/
>  System/Library/FrameWorks/UIKit
> 
> 
> 

and I have updated my target and project settings to point to that new framework location, but still when I build it, no luck.

I have also tried clearing out the simulator's applications and settings, still no luck.

The referencing .app is cleared when I run the "clean" menuitem, I have confirmed this, so clearly something in my project settings are still pointing to use the old UIKit location.

**Where should I be looking?**

I've gone as far as I can to help myself but I'm afraid I'm at a loss here. I don't see it under the target settings, or the project settings, or the plist, or any of the other files within my project.

Answer: 
I was getting the same error

dyld: Library not loaded: /System/Library/Frameworks/UIKit.framework/UIKit

The solution on my case was simply quit Xcode and try again.
I have had some similar problems with Xcode that seem to have no apparent cause. The fact of the matter is that Xcode does still have bugs here and there and sometimes you WILL run into a wall. 

**My Experience:** Similar to your situation somewhat, on one particular occasion, an Xcode project I was working just stopped building for whatever mysterious reason, and no amount of cleaning, googling or SO-ing provided me any answers. So I simply created a FRESH, NEW project and filled the source-code from my corrupt project into that of the new project. The new project used the SAME source, libraries, resources, settings, mind you -- and yet it built with no problems. It took about 20-25 minutes to make the transfer but considering that I had spent several HOURS trying to address a bug that would not reveal itself in the corrupt project, the time was well worth it.

So, I'd suggest doing what I did: Maybe try creating a fresh project and transfer your old source and resources over.

Good Luck