good tip randompete !
I checked the logs and found in the debug log file an entry ".. No loader found for extension "orchardtaxonomies"
Although the project name is Contrib.Taxonomies the directory name (on my system) is orchardtaxonomies (default one from the codeplex download). I excluded the project from the solution, renamed the directory to "Contrib.Taxonomies" and added to project
again to the solution.
restrarted and the taxonomies menu item appreared in the admin !