When i launch the use case complete example listed here http://plantuml.com/use-case-diagram i get an "IllegalStateException: Cannot find color #000005".
I set the GRAPHVIZ_DOT variable but can't get this to work.
The png error: https://imgur.com/z4z3rKm
Did you compile GraphViz yourself ?
This typically happens when some library are missing while compiling GraphViz (for example libexpat ) See http://plantuml.com/faq