error when adding fillets onto a polygon

Hi all;
I'm trying to add fillets onto the four corners of a rectangle polygon. But the program reports error after I adding the fillets. Please can anyone help me to identify the mistake? Mannnnnny thanks!!!!
//Vertices of the first square
gp_Pnt E(0,10,0.0);
gp_Pnt F(0,0,0.0);
gp_Pnt G(10,0,0.0);
gp_Pnt H(10,10,0.0);
//Construction of the fist square
BRepBuilderAPI_MakeWire wireMakerb;
wireMakerb.Add(BRepBuilderAPI_MakeEdge(E, F).Edge());
wireMakerb.Add(BRepBuilderAPI_MakeEdge (F, G).Edge());
wireMakerb.Add(BRepBuilderAPI_MakeEdge(G, H).Edge());
wireMakerb.Add(BRepBuilderAPI_MakeEdge(H, E).Edge());
BRepBuilderAPI_MakeFace faceMakerb (wireMakerb.Wire());
TopoDS_Shape B = faceMakerb.Face();

BRepFilletAPI_MakeFillet afillet(B);
TopExp_Explorer ex;
for(ex.Init(B, TopAbs_EDGE); ex.More(); ex.Next())
{
TopoDS_Edge medge= TopoDS::Edge(ex.Current());
afillet.Add(medge);
}

if(afillet.Shape().IsNull()) {cout TopoDS_Shape t= afillet.Shape(); //***************HAS ERROR ON THIS LINE!