Here is my code that keeps giving me that error:

param n;

param m;

param R {i in 1…m, j in 1…n};

param p {i in 1…m};

param delta;

var x {j in 1…n} >=0;

var rP;

var d{i in 1…m};

var r{i in 1…m};

minimize ADR: sum {i in 1…m} d[i]*p[i];

subject to return {i in 1…m}: sum {j in 1…n} x[j]*R[i,j] = r[i];

subject to sum_x: sum {j in 1…n} x[j]=1;

subject to total_return: sum {i in 1…m} p[i]*r[i] = rP;

subject to returns: rP >= delta;

subject to downside {i in 1…m}: d[i] = max(0,-r[i]);

Can someone help me find the problem please?

Thank you!!