Each stage other than stage 0 of a stochastic programming model must have at least one random variable assigned to it.  Random variables are assigned to stages using the @SPSTGRNDV function, which has the following syntax:

@SPSTGRNDV( STAGE, VARIABLE_NAME);

You will need to assign a random variable to the specified stage or reduce the number of stages in the model.  For more information on identifying random variables and associating them with distributions, please refer to the Language Features for SP Models section in Chapter 14.