A couple of ideas...
1. Run bin\sqldeveloper.exe directly from a command console window and see if you get any errors / stack trace.
2. Upgrade to at least 4.0.3 or the current 4.1.1. There were several bug fixes in the Scheduler made post-3.2, maybe this is one such case.
Also, with 4.1.0 or 4.1.1 (if the problem still exists) the new Statement tab in the Logging pane will show you all the SQL statements that get run. You can determine if it is the SQL which is not returning the data rows necessary to build the diagram. If so, maybe the import was somehow incomplete.
I managed to resolve this. It turned out that there was something wrong with the rules in the database... I overlooked that one case solved