Sorry, must have missed it. It was nearly 1AM when I wrote that.
To answer your question, when Python (and nearly all languages) encounter an "error", such as a constant missing, it will stop working. So any code that would have run after the error isn't run anymore. As a point of interest, there are languages where it's possible to "go on", but that usually results in totally undeterministic and therefore unpredictable behaviour. Which isn't what you want from a computer.
So what happend is that during the loading of the planets the Transport was loaded, which failed, which stopped the remainder of planet loading.