I got this error just recently when i tried to use the instrument to profile my iPad application on the device. And when i selected "Profile" from the menu, and instrument was opened. Then i selected "Allocations" or "Leaks", i just heard "Funk" and then nothing happened. So i checked out the Console and found out some errors about missing plug-ins for these selected functions. So bascially, it's because some plug-in in your Xcode application folder was missing or crrupt. So better remove Xcode completely through Command line "sudo /Developer/Library/uninstall-devtools --mode=all",then reinstall it. You should be good to go.
Then when i rerun my app with instrument i received another error which was the topic of this post. After searching a little bit. It's actually very easy to fix.

1.Make sure, the "Profile" scheme is using "debug" not "release" build configuration

Here is the way how to change it: In Xcode4, select "Product/Edit Scheme" from the top menu then click on the "Profile" button on the left panel. Under the "Info" tab you will see "Build configuration", make sure "Debug" is selected.