I assumed you were using 0.8 because you linked the example code for that version.
TGUI 0.7 and 0.8 are not compatible at all, although this simple example compiled, it did something completely different. The "50%" means "parent.width / 2" in 0.8 while it means "50 mod 0" in 0.7. The division by 0 might somehow be causing the crash. I have been able to reproduce it in 0.7 and will fix it in 0.7.6 as the code shouldn't crash for something like this.