I keep getting error 149 whenever I use set i. Why is this happening?

free variable cost;

set

i/1*12/;

Parameter

demand(i) /1 1000, 2 2000, 3 1500, 4 800, 5 2500, 6 2000, 7 1750, 8 2900, 9 900, 10 3500, 11 4000, 12 2000/;

NonNegative Variables Inv(i), W(i), H(i), L(i), C(i), S(i), PR(i), POT(i), PS(i);

equations obj, c1,c2,c3,c4,c5,c6,c7;

obj…

cost =e= 50*PR(i) + 52*PS(i) + 58*POT(i) + 2*C(i) + 3*S(i) + 300*H(i) + 400*L(i);

c1…

40*W(i) =e= PR(i);

c2…

2.5*W(i) =e= POT(i);

c3…

W(“1”) =e= 50;

c4…

W(i) - W(i-1) + H(i) - L(i) =e= 0;

c5…

Inv(“12”) =g= 700;

c6…

S(“12”) =e= 0;

c7…

PR(i) + PS(i) + POT(i) + S(i) - S(i-1) - Inv(i) + Inv(i-1) + 1000 =e= demand(i);

model number5 /all/;

solve number5 using lp minimizing cost;