Nevermind...I found it 🙂
When dealing with POST, you declare it as such:
for example: $_POST['userName']
In your case, what is happening is that you are trying to access a regular local variable in hiUser.php (which obviously does not exist).
Glad you found it.
a) Don't forget to flag this thread as 'resolved - found in the 'Thread tools' drop down menu along the top.
b) For future reference, when you edit leave your initial message there and simply append your new message to it. If other people just learning stumble across this thread (and have the same or similar issue you are having), they will not understand the context of this post.