The model contains an @MAX or @MIN function that has no arguments.  An example of this situation is:

MODEL:

SETS:

S1/1..5/: X;

ENDSETS

THEMAX = @MAX( S1( I) | I #LT# 0: X( I));

END

Note that the index variable I will take on values 1, 2, 3, 4 and 5.  In no case will I ever be less than 0.  This means that the condition (I #LT# 0) on the @MAX function will never be satisfied, meaning that there are no explicit arguments to the @MAX function.  Please check that all the @MAX and @MIN functions in the model are correctly specified.