Hi Craig...
I Don't know if my solution is the correct one.
what did I do??:
I Changed in SDP the way I define primary samples, right now I'm using scheme procedure (without valiration) ...for any lot size I have 20.
The sampling procedure assigned to the plan, use scheme procedure to valorate the samples.
Maybe, the reason for it works now, is because the sample is determinated and valorated with scheme procedure. (this is my conclusion).
Regards!
Daniela