I got a reply from a programmer, but she isn't familiar with Nirvanix. She gave the following suggestions, so could you please look it over and give feedback? Thanks!
/* Style Definitions */
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After observing "download.php",
my opinions are as follows：
1.Check whether the SESSION
Variable: userData exists
In your code：
header( 'Location: index.php');
I guess there is a problem when setting the value of "userData" , so
you always see the index.
Maybe you can print userData on the screen to see what it is and try to correct
2.Move the line: "session_start();
" to line2 ; (under "<?php")
3.About some variables：
You have to save the value into variable rather than take them as array's