So, the simple grammar was too complicated for them?
How willingly they participated? Were they aware about the experiment?
Most people I know would not be able to participate in any linguistic experiments -- it's just too difficult to... uhm, be conscious about grammatic nature of what they speak.
Steeven, stop torturing people. You should not enforce on them any words or rules, you should passively observe and take notice what kind of pidgin they'll develop -- most likely something heavily influenced by English.
