This is due to windows unable to manage partitioned flash drives.
Ok well,Thanks @Abhiram ShibuThis is due to windows unable to manage partitioned flash drives.
To solve this issue
1) Open a CMD as administrator ( click on start, type CMD, right click on cmd, run as administrator)
2) Type list disks (Find the disk with 16 gb capacity eg disk 1)
3) Type select disk 1 (In this example disk 1 is the target)
4) Type clean (Warning: this will erase all data in disk)
5) Type create partition primary (A new partition will be created)
6) Reconnect usb drive, u will be prompted to format it.
7) Format and enjoy 16gb goodness....
Typed using smartphone, please ignore if there are any spelling mistake...
I hope that fixed it