I assume you are talking about a bare Zip drive, not one already in an enclosure, right? If so, check the specs for your generic USB adaptor to see if it mentions supporting ATAPI devices & as well as ATA/SATA ones. Not all do. If it doesn't mention ATAPI specifically, or say something about supporting optical as well as hard drives, it probably does not support ATAPI.
You're right it's a bare ATAPI zip drive. As a I said it's a generic IDE/SATA adapter so it doesn't say anything on the manual or box but I found this on Apple System Profiler under USB Hi-Speed Bus:
USB to ATA/ATAPI bridge:
Bus Power (mA): 500
Speed: Up to 480 Mb/sec
Product ID: 0x2338
Serial Number: EE22D6D52722
Vendor ID: 0x152d
I've searching for JMicron 2338 but haven't found the tech specs
Maybe I need to install iomegaware to install a driver?
Thanks for all your help
It can't hurt to install the iomegaware software & see if it helps. Also, the user tip on this download page might be worth reading to see if it helps.
One other thought: most USB adaptors intended for bare drives include both a box with the SATA & ATA bridges in it & a power supply box, along with the appropriate cables. If yours does, make sure you are using the power supply & the furnished cable to power up the Zip.