Hi, I'm trying to use the concepts in the Kevin Bacon example in my code and am having trouble with compiling. http://www.boost.org/libs/graph/doc/kevin_bacon.html When I compiled the example by itself, it ran fine. However when I changed it to my data, then it gave me a compile error of "error C2106: '=' : left operand must be l-value" I don't know why this is, other than variable name, I just changed the vertex type from string to index. Nothing that I can see would cause this. The line not compiling is "grid_id[u] = gid;" See below for code. ************************************************************************ **************************** typedef property_map<ConnectionGraph, vertex_index_t>::type vertexID_MapType; typedef property_map<ConnectionGraph, edge_index_t>::type edgeID_MapType; vertexID_MapType grid_id = get(vertex_index, interfaceGraph); edgeID_MapType connectingElement_id = get(edge_index, interfaceGraph); typedef graph_traits<ConnectionGraph>::vertex_descriptor Vertex; typedef std::map<long,Vertex> NameVertexMap; NameVertexMap edges; for(CELAS2::iterator itr = CELAS2s.begin();itr != CELAS2s.end(); ++itr ) { long gid = (*itr)->getSideA_1Grid(); NameVertexMap::iterator pos; bool inserted = false; Vertex u, v; tie(pos, inserted) = edges.insert(std::make_pair(gid, Vertex())); if (inserted) { u = add_vertex(interfaceGraph); grid_id[u] = gid; <<<<-------- ************ this is the line that VS is saying non l-value. **************** pos->second = u; } else u = pos->second; } ************************************************************************ *************************** Any ideas why this is? I'm confused as to what's causing this. Any other way to populate the property map? I'm using VS2005 and boost 1.33.1. Thanks!