From 9.0.1FP8 document encrypt method changed (I think because of xPages). If you compile a code that has a simple call to a LotusScript library class that contains document encryption, its problematic.
Sample code (Script Library):
Public Class Encrypter
Public doc As NotesDocument
Dim session As NotesSession
Dim currdb As NotesDatabase
Set session = New NotesSession
Set currdb = session.CurrentDatabase
Set doc = New NotesDocument(currdb)
If you compile it with any Domino Designer below 9.0.1FP8, it works for all clients.
If you compile it with 9.0.1FP8, FP9 or FP10 it works in FP8-FP9-FP10 client, but failed to load script library on all previous clients (Error Loading USE or USELSX module Encrypter).
According to documentation, in previous versions, it has no parameters, but now it works with 0,1,2 parameters. We tried every combination, but still not working.