MIP error056

Hi,
I’m trying to use Gams to solve an engineering problem.In my model ,there are four rainwater storage tanks with initial rainwater,wasterwater updtream and a WWTP downstream.To minimize the emptying time of storage tank,I set state of storage tank as binary variable.The outlet flow of three storage tanks is controlled by water head,the other one controlled by pump with fixed flow.When I use MIP solver,it encounter error 056 Endogenous operands for * not allowed in linear models,when i change noliner solver, it encounter error 057.
Thanks to those who will help me.
1011yuhou.gms (1.65 KB)