GraphLayer gl[5];

Worksheet wks;
wks.Create();
GraphPage gp[5];
for (int j=0; j<=4;j++){
 gp[j].Create();
}
GraphLayer gl[5];
DataRange dr[5];
for (int i=0; i<=4;i++){
 dr[i].Add(wks,0,"X");
 dr[i].Add(wks,i+1,"Y");
 gl[i]=gp[i].Layers(); <-error
 gl[i]=AddPlot(dr[i], IDM_PLOT_LINESYMB);
 gl[i].Rescale();

}

void GraphLayer_AddPlot()
{
    Worksheet wks=Project.ActiveLayer();  // get the active worksheet
    
    for(int i=1;i<5;i++){
    DataRange dr;    
    dr.Add(wks, 0, "X");
    dr.Add(wks, i, "Y");  //plot the 1_ith columns as XY scatter
    GraphPage gp;
    gp.Create("origin");
    GraphLayer gl = gp.Layers();
    gl.AddPlot(dr, IDM_PLOT_SCATTER);
    gl.Rescale();
    gp.SetShow();
    }   
}