Here's a way to let you see what there is to see:
In the action file, add the line:
print_r($_POST);
It will dump the entire contents of the $_POST array - you can see what's there and what's not. Another thing to try: change the method to 'get' -and then you can see the results in the URL (don't forget to change how you reference(read) the data!).
A shortcut, by the way, is to retrieve $_REQUEST - which works for both post and get methods - it has a minor drawback (if both methods use the same name= for example) but it's not that easy to do without trying.
In any case - this lets you see what it is your sending and receiving - and don't forget that php is case sensitive.