[This is preliminary documentation and subject to change]
When setting the length property of an existing Array object, you specified an array length that was not a positive number or zero. This error occurs when you assign a value to the length property of an Array object that is negative or not a number (NaN). Note that JScript automatically converts fractional numbers to whole integers.
To correct this error
var my_array = new Array();
my_array.length = 99;