Could be just moisture that collected in the system, run it for a while with the heater fan on full but the a/c switched off then try it again, this will allow the evaporator to dry out completely, what I believe happens is that if you have the a/c on when the humidity is high the moisture can freeze onto the evaporator and then melts when the car is sitting giving dampness in the system which can also produce nasty smells
I usually run my D2 a/c on "economy" when not needed for just this reason as otherwise I find that you get a blast of damp air when you first start the engine which mists the windows up then you do need the a/c to clear it!