That program did not work. It errored out. I do, however,
have Rick Strahl's Registry.Prg.

My code is:

#DEFINE HKEY_CLASSES_ROOT -2147483648

CLEAR

SET PROCEDURE TO Registry.prg
oReg = CREATEOBJECT('registry')

oDll     = CREATEOBJECT("MyDll.MyClass")
cClassId = COMCLASSINFO(oDll, 4)
cClassId = "CLSID\" + cClassId + "\InProcServer32"

? oReg.ReadRegistryString(HKEY_CLASSES_ROOT, cClassId, "ThreadingModel")
? oReg.ReadRegistryString(HKEY_CLASSES_ROOT, cClassId, "(Default)")

RETURN

The first call to ReadRegistryString returns "Apartment", which is right.
But the second, to get back the Default key, returns null.

So how do I read the default key?