This item is from the Yet Another Enhanced IDE/Fast-ATA/ATA-2 FAQ, by John Wehman and Peter den Haan with numerous contributions by others. (v1.92).
The Win95 busmastering drivers sometimes have trouble co-operating with older harddisks and ATAPI CD-ROMs. Try installing the latest drivers.
If that doesn't help, you could try this registry hack. Move all old devices to the secondary port. Back up the registry (system.dat and user.dat in the Win95 directory). Start regedit and look for
Here is where the entries for both ports should be located. In the second entry, change the key PortDriver from "ideatapi.mpd" to "esdi_506.pdr". This will cause the secondary channel to be handled by the default driver.