The solution to this if you’re using the GUI on Linux can quite possibly be that ptrace_scope was set to 1.
From the Intel forums:
Note: In Ubuntu 11.4, you may need to disable ptrace_scope.
cat /proc/sys/kernel/yama/ptrace_scope; “0” is expected, if it is “1”,
$echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope
Took me a while to find… hope this saves someone some time.