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).
There are numerous reasons why this can fail; you will more easily be able to do something about it (or decide if you want to fix it in the first place) once you know some background.
Windows' 32-bit disk access (32BDA) is a bit of a misnomer, actually, since it has nothing to do with 32-bit data transfers. A slightly better name for it is 'FastDisk'. It is a feature of Windows in 386 Enhanced mode that allows one to replace the BIOS' disk routines by Windows' own routines that work in protected mode. A much better name, then, would be "protected mode controller access". For some reason Microsoft decided not to use the latter.
Anyway, the main advantage of this feature is that it allows Windows to use virtual memory for its DOS sessions. Without 32-bit disk access, DOS sessions cannot be swapped out and every DOS box takes 640k of real memory. Because it also reduces the number of switches between virtual and protected mode Windows has to make, it gives a slight performance improvement as well, but usually nothing dramatic. Only if 32BDA is used together with Windows for Workgroups' 32-bit file access feature, it will eliminate these mode switches altogether (at least for most disk operations), which gives a far more interesting performance boost.
Unfortunately, the standard FastDisk routines that are internal to windows, called *wdctrl, are severely limited in their capabilities. The *wdctrl software understands nothing of non-IDE hardware (e.g. SCSI), more than two harddrives, drives with more than 1024 cylinders, 32-bit host bus transfers, block transfers, or ATAPI CD-ROM drives on the primary channel. If you use any of these things, 32-bit disk access won't work unless you have a *wdctrl replacement.
Today, that means that 32-bit disk access won't work 'out of the box' for most of us.
Most interfaces that are incompatible with *wdctrl come with their own FastDisk routines (usually with a .386 extension). For the rest of you, many drive manufacturers offer replacement FastDisk software. Many drive manufacturers have such drivers on their WWW sites these days; take a look in the net.resource guide below. You can also contact your vendor to find out what is available. Last but not least, the ontrackw.386 driver in <ftp://ftp.ontrack.com/pub/software/> is reported to work fine on all drives even if you don't use Disk Manager.
Most of these drivers won't give you 32-bit disk access if you have an ATAPI CD-ROM on the same cable as the harddisk. Only a few CD-ROMs come with a special VxD driver which does the job.
Note: these drivers are incompatible with the Stealth feature of some versions of Quarterdeck's QEMM. Quarterdeck's fix can be found on <ftp://ftp.wdc.com/drivers/hdutil/>.