I think that your download center would work if you used the file name in the hidden form element rather that the location. If the file name is this: $row_WADAorderdetails['FileName'] then you should use that for the value of the hidden form element.
The code that I posted for you to add just after line 101 should look very close to the code that you already have on this line but it is different. The difference is that if you add the code that I posted it will stop the code from executing and print out a message about the values that are being referenced in the download function call. If you add this code in and do not see the message it would indicate that your download server behavior is not being triggered.