Missing Data After AJAX Call

I was working through the night last night, burning the midnight oil as they say, trying to get this AJAX deal to work. I had to fill a select field with options once the user selects an option from a second select field. But, every time I made the AJAX call to retrieve the data, the target select field remained empty… in IE. Argh! IE! Why do you haunt me so?!

I put an onChange call on the select field to call the Javascript function when the user selects a field from the dropdown: