My usb size is 8 gb. Out of this space i still have 7.2 gb free.

Now the issue is tht when i was copying a file of size 5.2 gb so it gave me error tht usb size is not that much and the file couldnt be copied.

Also i have scan my usb, formated as well but still the same issue. Kindly provide some usefull information to resolve this issue.

The file that i m copying is media file.

 

I think your USB has to be formated to UDF not fat32. Here is link on how to.
http://www.ehow.com/how_5863457_format-usb-udf.html

 

It's possible that your problem is not the USB stick but that the device you are plugging it into isn't giving it enough power eg an older laptop. My new stick will not work with my old laptop unless I supply power to it from the mains or a newish pc via a 'Y' cable. Try the stick on a different machine to see if it will work with more 'juice'.
Regards
Rob