I've been using Xcode 4.3.1 since it came out now and I've worked on many different projects since. Everything has always worked fine until this new project I'm working on.
The code completion/code sense never finds anything. When I 'Command+Click' a variable or class normally it would jump to that but now I'm just getting:
Symbol Not Found
The Jump to Definition action is not working.
If I open one of my older project while this bad one is open, the old ones still work for code sense and the new one doesn't.
My partner is working on the same project, we both get the files from our repository and the code sense works on his machine for this project...just not mine.
Try this:
Open the organizer. Close your project in Xcode (leaving Xcode and the organizer running). In the organizer, in projects, click on the Delete button next to Derived Data. Quit Xcode.
Find your Xcode project via the finder. Rightclick and "Show Package Contents". Delete project.xcworkspace and xcuserdata folder.
Open up Xcode again and see if that works for you.