fair warning. When you try to upload your song and it says The file you attempt to upload is invalid: (type of file), do the following steps.
1: first log in of course.
2: Go to where you saved your song.
3: Right click the file and re-name it.
4: out down this - (song name).note - Since the computer is very smart, it can also read any type of file. So putting down (.note) in the end of your music file, your computer will be able to change the file type to .note AKA notessimo's file type.
5: After re-naming, try to re-upload again and there you go!
P.S: Do not do this to any other file but your music file you are trying to upload. If you do this to any other file, you will mess up that file and that file will never be able to run again.