I think your problem is that all your verticies are at the same location.

From the documentation:

" Prior to invoking this algorithm, it is recommended that the vertices be

placed along the vertices of a regular n-sided polygon via

circle_layout<http://www.boost.org/libs/graph/doc/circle_layout.html>.

"

thank you so much, that was it.

i actually read the docs, but since it says "recommended" i thought i'd rather leave it away to make things not even more complicated.

i think i will suggest to have the documentation changed to "...it is required that...".

sebastian mecklenburg