I purchased a 4GB ZEN Korean Technologies MP4 player. Plugged it into my PC and it only had 233MB available. I sent it back and got one that showed up as having 4GB. But all files put on it beyond 233 MB were unreadable.
I suggest that when anyone buys a player they fill the memory up and check to make sure the last files you put on it are functional.
The ebay seller was "skatecellar"
*BTW I purchased another 4GB player (falsely advertised as Apple Ipod OEM), and it does, indeed, have 4GB. I have filled it to capacity and played the files with no errors.