Maybe you have exceeded the maximum number of files in the root directory. See if it's possible to create folders and put some tracks in them.
While you're at it, see if the player supports drag and drop transfer of files (there may be a switch in Settings called something like PC Link Mode).
I have a no name brand mp3/mp4 player...It can hold 8gb. I have an emachines t1842 with 1 gb ram and a 1.8gb processor. When I hook my mp3 player up to the computer and open up windows media player, everything is fine. I put the songs I want to sync in the list and attempt to sync. However, it will only load about half my songs. I get an error message for the rest of the songs. I have plenty of room on the player... they just won't load. The error message is.... error message C00D1236. When I research this... it states some of the filesmay be marked as hidden... I looked and they are not. Any suggestions on how I can bypass this and get my music on my player?