Posting Form Variables

I have a table with dynamic html that contains drop down select lists
and readonly text boxes. Dynamic calculations are done on change of a
value in one of the drop down select lists.

For my first iteration the script works fine ( indicating that there
are 33 form variables ). When trying another dropdown select value, the
form elements.length is shown as 33 ( as about ) BUT the script then
crashes with a 'null value' error. I cannot access any of the form
variables - this works in all other browsers and platforms.