Tinderbox 5.0.3 was released more the seven years ago.
It's difficult to know what the problem might be. I have 5.12.3 on my computer for the occasional tech support issue that still involves Tinderbox 5, but here we are already on 7.0.3 and testing the next release.
Of course, 5.0.3 was written for 10.6/Snow Leopard, so compatibility with 10.12/Sierra is an open question. My first guess would be to check to make sure that $Lock hadn't been set.