Environment:
Windows 10 64 bit
JDK jdk1.8.0_71

VStar execution:
Download 2.20.0 ZIP file and execute it with
java -verbose -splash:"vstar/extlib/vstaricon.png"  -Xms25m -Xmx500m -jar "vstar/dist/vstar.jar" 
I preiously have run Vstar from WebStart and have almost all current plugins are installed in my 
user directory (c:\Users\Name\vstar\plugins).  When I simply run VStar locally with the above command, 
it seems to work ok and all the plugins appear in the menus.

I then copied the ExampleObSource code from the PDF vstar_plugin_dev.pdf into a java file and
compiled it with 
javac  -Xlint:deprecation -cp vstar.jar my/vstar/plugin/ExampleObSource.java
jar -cf my.vstar.plugin.ExampleObSource.jar my/vstar/plugin/ExampleObSource.class

I got a warning about a deprecated method, getCurrentStarName, that I ignored. I copied the resulting
jar file to my user directory.  The I ran VStar, as above, and it fails during initialization as follows
[Loaded org.aavso.tools.vstar.ui.undo.UndoableActionManager$2 from file:/E:/Users/clk/Documents/Astronomy/Software/VStar/dev/vstar/dist/vstar.jar]
[Loaded org.aavso.tools.vstar.ui.IMainUI from file:/E:/Users/clk/Documents/Astronomy/Software/VStar/dev/vstar/dist/vstar.jar]
Exception in thread "main" [Loaded java.lang.Throwable$PrintStreamOrWriter from E:\Program Files\Java\jdk1.8.0_71\jre\lib\rt.jar]
[Loaded java.lang.Throwable$WrappedPrintStream from E:\Program Files\Java\jdk1.8.0_71\jre\lib\rt.jar]
[Loaded java.util.IdentityHashMap$KeySet from E:\Program Files\Java\jdk1.8.0_71\jre\lib\rt.jar]
java.lang.NullPointerException
        at org.aavso.tools.vstar.ui.dialog.MessageBox.showErrorDialog(Unknown Source)
        at org.aavso.tools.vstar.ui.resources.PluginLoader.loadPlugins(Unknown Source)
        at org.aavso.tools.vstar.ui.VStar.main(Unknown Source)

I repeated this with ExampleObSource and ASASObservationSource from 
https://sourceforge.net/p/vstar/code/HEAD/tree/trunk/plugin/src/org/aavso/tools/vstar/external/plugin/ 
and had the same initialization failure.  Note that I did remove the problem jar from the user directory
each time.

I then backed up to the ObservationCounter example and an error that the invoke
method now takes a different argument type appeared at complie.  I had taken the code from the PDF 
again and then downloaded the version from SourceForge.  This compiled and worked within VStar as expected.

Now I am aware that the package, jar filename and directory structure need to be in sync and have checked
this several times.  In fact I got them out of sync and experienced the same PluginLoader error during
initialization.  I wonder if you have any suggestions as to other things to look for.  I suppose I could
download the whole VStar source, install Ant and build it locally so I could run it under the debugger.
However, that would be a significant amount of work.
Cliff Kotnik
clkotnik@att.net