Formatting a 3.5" disk on a //c+

[randrews <randrews@pdq.net>]

I have an Apple //e and an Apple //c+. I have gotten a copy of DOS 3.3
to boot both of these, but the copy is on a 5.25" disk. The //c+ has a
3.5" disk drive, I and I want to somehow format a 3.5" disk to boot it
from. I read in the new FAQ (posted here) that I need a double density
3.5" floppy, but I am simulating this by covering up the hole in the
left corner.
To format the disk I'm saying INIT HELLO,S5,D1 after booting from the
DOS floppy. All I get is I/O ERROR. Why? How is this done?