"This script or class was runnable but could not be run"

I'm getting this error when running a groovy script (GroovyRuntimeException), and the top Google results are not clear/concise enough. What exactly does t开发者_Go百科his error mean?

Looking at the source, the script class does not have a main method and one of these is true:

• It has neither a parameterless constructor not one that takes a String array
• Or the constructor threw an exception

The stack trace should tell you which.