well, your code has a couple of major problems....
with combo boxs, you want to use the setChangeHandler() method, or just type the function name into the changeHandler property in the property panel.
so here is what you do:
1. delete the code out of the changeHandler box in the property panel.... leave it blank.
2. all the code on the first frame of your main timeline with this code:
3. you had a problem with the path to your text box. the text box was inside of a movieclip, so your path name needs to be: mc_name.textField_name.text (or htmlText) in this case.
4. don't know what the textformat object is set up for, your not using it anywhere.