Jquery Autocomplete Script Problem

Jquery Autocomplete Script Problem

Hi,
 
I'm using Autocomplete Plugin to fill a drop down list and It gives me some errors.I have attached my codes in to this.In my code you can find  "year of birth" text box and "user" autocomplete box.I need to manipulate "user" list according to value of "year of birth". In that case first time it seems ok. (First I enter a value to "year of birth" then "user" box should manipulate with related users).  Then I enter a new value to "year of birth" and go to "user" box, it shows me both lists which related to first value and second value. It means first list not cleared.
Any help on this will be highly appreciated.
 
Thanks,