Driver problem with CD/DVD?

My CD/DVD drive (Lite-On LDW-451S) is giving errors like "whatever.EXE is not
a valid Win32 application" and "error performing inpage operation" when I try
to run programs or copy files. But there's no physical problem with the
drive or CD media.

I can boot from the drive. In fact, I did a fresh install of Windows 2000
on another partition, USING THAT DRIVE. The drive works fine from the test
install, using various CDs.

In Windows, I've uninstalled and reinstalled the drive, reloaded the
driver--no joy. The system did have Sonic DVD software installed; _after_ I
started having a problem I uninstalled all of that as well.

I hadn't used the drive for several weeks before I noticed the problem, so
I'm not sure what might have been altered in the system. My event logs show
no errors related to the drive, and no errors of _any_ kind over the last few
days.

I've searched the registries for my main Windows installation and my new
test installation, and found a few differences.

In HKLM\SYSTEM\CurrentControlSet\Enum\IDE, the drive's ActiveService value
was set to "cdralw2k" (from Sonic/Adaptec) instead of "cdrom". I cleared the
UpperFilters and LowerFilters values from the "CDROM" class in
HKLM\SYSTEM\CurrentControlSet\Control\Class, and now ActiveService is "cdrom"
on both systems, but the drive still doesn't work.

Any ideas what else I could do to track down what's blocking this drive from
reading?

Thanks a million!
Jay