you don't have a blank option for the subcategory.
when i search for automotive and don't make a selection in the subcategory, the search page URL is:
http://palmbeachgrapevinedirectory.com/ResultsForBusinessCSL.php?Parent=14&Child=Choose&Location=&Submit=Search&WADbSearch1=Submit&WADbSearch2=Submit
so it is passing Choose as the subcategory.
if i set the subcategory to be blank:
http://palmbeachgrapevinedirectory.com/ResultsForBusinessCSL.php?Parent=14&Child=&Location=&Submit=Search&WADbSearch1=Submit&WADbSearch2=Submit
it seams to work as desired.