In my graph there is a path between vertices 5 and 36 but when I run query:
match (n {Id:5}), (m {Id:36}), p=shortestPath(n-[*]->m) return length(p);
I came across this same problem, and I found out that if you don't inform the maximum hops, the shortestPath will limit the maximum hops to 15. I'm using neo4j 2.2.1