I\'ve just started playing with Xcode 4, and found that, no matter how I setup debugging symbols in the project, Instruments refuses to display source lines for stack trace item
Here's my environment...
I had the same problem running in the simulator, and it was driving me nuts because ALL the standard go-to fixes were not working.
What did it for me was plugging my iPad into the MacBook and running an instruments session against said app on my plugged in iPad. Instruments properly symbolicated my app when running on the iPad, and then continued to work when I disconnected the iPad and ran instruments later in the simulator.
I suspect it had something to do with updating my project to use the following...
I don't know why that would be the case, but that was the ONLY project change I had made before my symbols were lost in Instruments.