In PROC MODEL, if a parameter name is the same as a general form equation name that appears after the EG.-prefix equation, and the equation is specified in the SOLVE statement, this equation is ignored in the SOLVE task and can cause either one of the following errors in the log:

ERROR: The system of equations cannot be solved because it contains one or more underdetermined components with fewer equations than solve variables.

ERROR: The number of variables to solve for does not equal the number of equations that the solution is to satisfy.

To circumvent the problem, rename either the parameter or the equation so that they do not have the same name.