I've had this happen a few times on SuperDisks I bought at CompUSA. To let you know which revision of the SuperDisk drive I own and use on my iMac333 is the Bondi-SuperDisk drive(originally bought for my iMac266).
First try reformatting it with MacOS, I had luck on my first few tries with one disk, and on the second it did the same so I tried Norton Util 5.0 or whatever the newest one is, found out NU can't mount or see USB devices so I tried Alsoft's Diskwarrior. DW saw the floppy and tried to repair it, nope it didn't work(argh!).
I then ran over to my PIII and plugged the drive to the USB port and installed Imation's drivers from Superdisk.com and formatted the disk with my PC. After the format was done I unplugged the drive from my PC and took it to my iMac and the disk reformatted to MacOS HFS+. I could have done it using VPC but disk formatting is slooow. Its also a good idea to check superdisk.com every so often for new drivers and check their tech notes.
I hope this helps