There’s a lot of fake memory floating around the web at the moment, including big sized usb drives that appear to have say 32GB of memory, but have been “hacked.” When filled up to 4GB the rest of the files become corrupt. This is the same with mp3 players and other flash memory.
If you have purchased one of these drives on ebay or paid through paypal you can generally get your money back if you file a complaint with paypal saying wrong product received etc..
To view my ebay guide on usb drives please visit here.
To check the true memory size please use the following utility. This program writes data to the drive, then reads it back to show the true size of the drive.