There is an error in the documentation (6000PG) for the SetNTMultiCardAddress function of the nt6400.dll. The function should be declared as
Declare function SetNTMultiCardAddress Lib "nt6400.dll"
(ByVal address as Long) as Boolean
The most common symptom of this error is that only the first card (lowest address) in your system will be recognized, regardless of what addresses are used, or what order you attempt to initialize them in.