putpkt: write failed, broken pipe
This problem seems to happen whenever I quit the app on my device (pressing the home button) while the debugger is stopped at a breakpoint. Any subsequent build and run on my device results in this error.
To fix this, there's no need to delete the app, clean or rebuild. Just need to restart the device.
Well, I've restored my iPad to factory defaults. And it seems to work now, so yeah.
EDIT: Please look at @mud's answer below since it solves most cases without a complete restore. In my case that didn't work, so I've accepted this answer.
I had the same error - I not only restarted my device, but also deleted the app on my device and cleaned the build directory (product --> clean on Xcode 4).
I then built and ran the program again and it worked.
I did not need to restart Xcode.