Workflow examples are stored in the 'examples' subdirectory of your Taverna installation. The following workflows are known to have problems:
AlternateExample.xml
FetchDailyDilbertComic.xml
FetchGbrowseImageSelectTracks.xml
An up-to-date set of workflow examples can be found in the Taverna 1.7.1 starter pack on http://www.myexperiment.org/packs/14
Additional workflows can be found by browsing on http://www.myexperiment.org