Help with Cplex.

Hello ,
I need to check if this program in cplex is correct. There is a
quadratic constraint. Cplex prints out the ERRR message.

The code is :

#include <ilcplex/ilocplex.h>
ILSTLBEGIN

typedef IloArray<IloNumVarArrayNumVarMatrix;

int main()
{
IloEnv env;
try {

IloInt i, j;
IloModel model(env);


IloInt D = 4;
IloInt M = 10;
IloInt K = 2;


IloNumVarArray d(env, D, 1, M-1,ILINT);
IloNumVarArray b(env, M-1, 0, 1 ,ILINT);


NumVarMatrix a(env, M-1);

for(i = 0; i < M-1; i++)
{
a[i] = IloNumVarArray(env, D, 0, K, ILINT);
}




// Formulas

for(i = 0; i < M-1; i++)
{
model.add( i+1 == a[i][0]*d[0] + a[i][1]*d[1] + a[i]
[2]*d[2] +a[i][3]*d[3] );
}


//Constraint
for(i = 0; i < M-1; i++)
{

model.add(a[i][0] + a[i][1] +a[i][2] +a[i][3] <= K);

}

for(i = 0; i < M-1; i++)
{
model.add(b[i]<= a[i][0] + a[i][1] +a[i][2] +a[i][3]);
}

IloExpr obj(env);
for(i = 0; i < M-1; i++) {

obj = b[0] + b[1] + b[3] + b[4] + b[5] + b[6] + b[7] + b[8] +
b[9] ;
}
model.add(IloMaximize(env, obj));

IloCplex cplex(env);
cplex.extract(model);
cplex.solve();

env.out() << " Solution: " << endl;

env.out() << " " << Value() << endl;

} catch(IloException& e) {
cerr << "ERRR: " << e.getMessage() << endl;
} catch () {
cerr << "Error" << endl;
}
env.end();
return 0;

} // END main