...
if (check_xyz(item->mx, item->my, req->z, &(maps[i]))) {

    ######## START OF MY CODE #######
    try {
        maps[i].map = Map(256,256,maps[i].map.srs());
        mapnik::load_map(maps[i].map, maps[i].xmlfile);
    }
    catch (std::exception const& ex) {
        syslog(LOG_ERR, "An error occurred");
        maps[iMaxConfigs].ok = 0;
        break;
    } catch (...) {
        syslog(LOG_ERR, "An unknown error occurred ");
        maps[iMaxConfigs].ok = 0;
        break;
    }
    ######## END OF MY CODE ########

    metaTile tiles(req->xmlname, req->options, item->mx, item->my, req->z);
...