Itz about a pendrive which ive bought now.....?

hey!! ive just bought a 16 GB pendrive (kingston)...ive kept ! GB movie in it and tried to keep a 7.2GB blu ray muvi since it had 13 GB free space in it....but when i tried to copy and paste it it is showin disk drive full!!! RETRY.....but other movies are finely going into the pendrive so whats the problem and what shoud i do????????????????