VB API Tool Kit for Assembly Drawing from Part Drawing

What needs to be modified in the existing VB Program syntax to refer
assembly drawing since original API Kit was developed to refer part model
drawing.

Note: API Kit is working well for part model drawings. Refer below for the
coding which created to read part model in the drawing.

DimasyncConnection As IpfcAsyncConnection = Nothing
Dim conn As CCpfcAsyncConnection
Dim session As IpfcBaseSession
Dim model As IpfcModel
Dim assembly As IpfcAssembly
Dim tableOwner As IpfcTableOwner
Dim tables As IpfcTables
Dim table As IpfcTable

conn= New CCpfcAsyncConnection
asyncConnection = conn.Connect("", "", ".", 5)
session = asyncConnection.Session
model = session.CurrentModel
assembly = model
tableOwner = assembly
tables = tableOwner.ListTables
table = tables.Item(0)

Here is the sample code. I am trying to chenge the assembly drawing.

I am getting some exception. I have attached the exception.