Although it should be letting you download more than 424mb of files, there are only 2 things I can suggest:
- Try to open up the folder when you plug it into your computer. Search through the folders and see if there are files in there that may not be compatible with your mp3 player and therefore will not display.
- Check for duplicate files and that the size of the files is not misleading. I've had a problem where a certain song was displayed as being 2.56mb, I opened it on my computer before it was transfered and it was registered as 60mb because the track would continue to play for hours afterwards because of the file being inappropriately labeled at the ending point.
The fact that there is so much unused and unusable space on the mp3 is unusual, but you may have a problem also with your formatting. You DO have to leave some space in your mp3 player to leave room for the operation files of the mp3, so although it is labeled as having 2gb of space, you have to save at least a couple mb of space to let the system function. Hope this helps.