This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
A solution is "goosing" the drive by manually ejecting and reinserting it. Apparently, using the SCSI driver for the Apple Card that was sold by Tulin Technologies solves a lot of troubles with the Apple card and a Zip drive. You can get the Tulin SCSI driver from Mr. Wing Chung (104465.3171@COMPUSERVE.COM) for $20. By: Rubywand