"International students in F-1 and J-1 nonimmigrant status who have been in the United States more than 5 calendar years are resident aliens and are liable for social security/medicare taxes. When measuring your date of entry for the purposes of determining the 5 calendar years mentioned above, the actual date of entry is not important. It is the calendar year of entry which is counted toward the five calendar years respectively. Thus, for example, an international student who enters the United States on December 31, 2003 counts 2003 as the first of his/her five years as an exempt individual."

src = http://www.uc.edu/international/services/taxes/social_security_medicare_refund.html

if you have already been  in US for over 5 yrs, then you asked for the refund of SS and medicare tax which you sholdn't have