Oops, you should change it to hex-value 00 - not 30.
Still I have no idea why the player freaks out like this...

Maybe you opened the file in notepad or a text-editor and saved it from there - this would definitely screw up the file, even if you didn't change anything.
The edited file's size should be exactly the same as the original file's.
And don't forget to set the player back to read-only after uploading the file - you should really do it step-by-step.