To flash back to stock you have to first download odin here www megaupload com/?d=M6CO8E1K .
Then you need the stock ROM, the US Version is here www multiupload com/681518H5EF, assuming you have the US version of the galaxy player, if not you can find the rom around somewhere but I am unsure where.
Now, put the player in download mode by holding Power, Volume Down and Home at the same time for 5 or so seconds and connect it to your pc. Odin should now detect your device.
Next click on the PDA button and navigate to the file with the extension .tar.md5 extracted from the stock from.
After that click start and it should flash the stock rom.
Make sure that the option "Re-Partition" is NOT checked in Odin before you flash only Auto Reboot and F. Reset Time.