When I was making disks on my PC to install programs on my Classic II I ran into the same problem. My classic II spit every disk back out at me, even if I tried to initialize the disk on the classic II the init would fail every time regardless of how many different disks, different brands, even different manufacturing years I tried.

The only thing I found that worked was to use the SoftMac XP emulator to format the disk on my PC, then I put it into the classic II, which still said it was crap but the initialization of the disk actually worked now, then I brought it back over to my PC and used RaWrite to write disk images to the disk. After that my Classic II had no trouble reading the disks.

I haven't been able to come up with a good reason why this method works. I have a feeling it has something to do with the low level format of the disk, but that's just a guess.