[Scons-users] Issue with scons on AIX - what is error 6?

[TOM TANNER (BLOOMBERG/ LONDON)]

one of my builders runs a c++ program and checks the output. The C++ program looks a bit like this:

int main()
{
    int res = some_func();
    std::cout << "res is " << res << std::endl;
    return res;
}

and SCons says this:
res is 0
scons: *** [path to my program] Error -6
scons: internal stack trace:
  File "/opt/swt/install/scons-2.1.0/lib/scons-2.1.0/SCons/Job.py", line 201, in start
    task.execute()
  File "/opt/swt/install/scons-2.1.0/lib/scons-2.1.0/SCons/Script/Main.py", line 183, in execute
    SCons.Taskmaster.OutOfDateTask.execute(self)
  File "/opt/swt/install/scons-2.1.0/lib/scons-2.1.0/SCons/Taskmaster.py", line 243, in execute
    self.targets[0].build()
  File "/opt/swt/install/scons-2.1.0/lib/scons-2.1.0/SCons/Node/__init__.py", line 372, in build
    self.get_executor()(self, **kw)
  File "/opt/swt/install/scons-2.1.0/lib/scons-2.1.0/SCons/Executor.py", line 358, in __call__
    return self.do_execute(target, kw)
  File "/opt/swt/install/scons-2.1.0/lib/scons-2.1.0/SCons/Executor.py", line 343, in do_execute
    raise status
scons: building terminated because of errors.

What is error -6? and why is it coming up when my program has returned zero.