sharepointer used as a value - error during assignment

I have a sharepointer defined like this

boost::unordered_map<int,share_ptr<boost::unordered_map<int,string>>> webData;

...
webData[100]=share_ptr<boost::unordered_map<int,string>(new boost::unordered_map<int,string>(make_pair(100,"json data returned")));

I always get error at this webData line no instance of boost::unordered_map<K,T,H,P,A>....matches the argument list