javascript抛出未捕获的TypeError:无法在填充多维数组时设置未定义的属性“0”

I am debugging a 5-odd-year old script and this is driving me nuts. None of the answers I found could help me pinpoint the error. I have made a new Version after reading up on Arrays. Neither the position nor the "timing" of the Exception makes any sense to me whatsoever...I am debugging a 5-odd-year old script and this