Reader X plugin error only on XP?

My company has a Reader X / XI plugin that worked fine when we built it with VS2005, but recently updated the project to VS2010, and now it throws a Class not registered com exception when it loads, but only on Windows XP (32 bit).  Works fine on Windows 7 (64 bit).

The code that throws is loading a COM object that is a DLL in our install directory that is registered on installation of our product. The code to do the registration is identical for Win7/WinXP. The registration in the registry appears to be identical (except for paths etc) on both machines.

We create a whitelist file on install, and set the registry FeatureLockDown/bWhiteListConfig value to 1.  As I said, it works fine on Win7, and the code is identical (other than correcting the paths as necessary) for WinXP. This same code worked fine when we were building with VS2005.

Here's the whitelist file contents:

; Files Section

FILES_ALLOW_ANY = C:\Program Files\<our_install_dir>\*

FILES_ALLOW_ANY = %appdata%\<our_app_dir>\*

FILES_ALLOW_ANY = C:\Documents and Settings\<user>\Local Settings\Application Data\<our_app_dir>\*

; Processes

PROCESS_ALL_EXEC = C:\Program Files\<our_install_dir>\*

PROCESS_ALL_EXEC = %appdata%\<our_app_dir>\*

PROCESS_ALL_EXEC = C:\Documents and Settings\<user>\Local Settings\Application Data\<our_app_dir>\*

; Registry

REG_ALLOW_ANY = HKEY_LOCAL_MACHINE\Software\Adobe*

; Mutants

MUTANT_ALLOW_ANY = ms*

MUTANT_ALLOW_ANY = ol*

///// the DLL name we're trying to load starts with Ta

MUTANT_ALLOW_ANY = Ta*

; Sections

SECTION_ALLOW_ANY = ms*

SECTION_ALLOW_ANY = local*

; Events Section

EVENTS_ALLOW_ANY = ms*

EVENTS_ALLOW_ANY = gl*

EVENTS_ALLOW_ANY = _fc*

; Named Pipes Section

SECTION_ALLOW_ANY = ms*

; Dirs Section

FILES_ALLOW_DIR_ANY = C:\Program Files\<our_install_dir>\*

FILES_ALLOW_DIR_ANY = %appdata%\<our_app_dir>\*

FILES_ALLOW_DIR_ANY = C:\Documents and Settings\<user>\Local Settings\Application Data\<our_app_dir>\*

Any help would be much appreciated.