The songs that you loaded onto the player are not in the correct format - iTunes, DRM-encrypt. WMA are not allowed, for instance. Convert everything to mp3 format. It is asking you to reformat the player because it wants you to delete the wrong-formatted songs off the player. I would check your user manual to find the best way to reformat.
In general, though, there are two ways to format an Mp3 player - one on the computer
itself, and one in Windows Media Player. Both methods will end up
erasing all the songs on the player, but the player will be "good as
new" after that. Sometimes reformatting in this manner will override
the player's native formatting and cause problems - this can be
reversed in most cases by updating the player's firmware. Firmware
upgrades are available from most manufacturers' websites.
WARNING: The following procedures will erase all songs on the player.
Check if the file system is NTFS. If yes, format it to FAT or
FAT32. - Connect player to computer, double-click my computer, right
click on icon of mp3 player and select format. This only applies to
You can also format the player in Windows Media Player itself:
Connect your Mp3 player to the computer and open Windows Media
Player. Click on the Sync tab. Pull down the drop down menu underneath
the Sync tab by moving your cursor over the Sync tab and left clicking
on the little black arrow underneath the Sync tab. Highlight "name of
Mp3 player here 1GB" (wording may vary slightly), and then select
"Format." - this should erase everything.
-Tha Mp3 Doctor