Perhaps this topic will be helpful:
adding a property does not by default initalize (except in the case of simple number (0) or strings (""))
other object such as a database need to be instantiated ( db = new SQLitedatabase for example), but even that while creating an instance of the database does not connect it to a database structure ( DB.CONNECT)…
Nope.
If the property is a simple data type like an integer, you can just go ahead and use it.
Classes such as SQLiteDatabase, folderitem, dictionary… they all need to be initialised.
Usually in App.open event
If not there, then ‘just in time’ like this
if App.DB = nil then
msgbox "The DB object had not been initialised by this point"
App.DB = new SQLiteDatabase
end if
At the error point Session.DB is nil. This has nothing to do with the folderitem.
Before the If End If block insert the line
Session.DB = New SQLItedatabaseIn your If Else section you are missing a connect statement
If Session.DB.Connect = False Then
Msgbox ("Database file Exists, but can't connect to it")
End If
Remove the lines
Dim db As New SQLIteDatabaseIt is not used and could be confusing and
Session.DB.DatabaseFile = NewDatabaseFilenear the end.
You should also insert error checking after each SQLExecute and after Commit.
Your placement of the database file in the resources folder is going to cause you problems when run in the Program Files folder as resources will be read only. I would use applicationdata instead.
HTH
Wayne
Remember, you can’t use the global Session function in a Session.Open event. (source)
There’s your NOE 
(Thanks to Wayne who pointed out the obvious, that Session was nil. Wouldn’t have seen it otherwise.)