it is the .serialize() which is creating problem, because it convert the form data into string, thats why $_FIELS doesnt contain anything.
I think i have figured it out.
http://stackoverflow.com/questions/8971261/php-5-4-call-time-pass-by-reference-easy-fix-available as reference.
Just remove the word “&” and it will work for you.
Atleast it is working for me.
Cheers