While trying to use a Scripted Data Source within BIRT Report Designer I ran across this error:
Where OBJECT is any Java class. My Java class was very simple.
I verified my JAR file was in the plugin scriptlib folder
My problem was that my Java class had a main signature for some simple testing outside of BIRT.
I removed the main method on the class and exported my JAR again.
BIRT Report Designer could then instantiate my Java class without error.