"ch.qos.logback.classic.gaffer.GafferConfigurator:48" creates a GroovyShell() without specifying the classloader. When I have a Groovy application using Logback with Groovy config and it is retrieved with Groovy @Grab, where CL hierarchy is somewhat different from a usual invocation, the execution fails, error log is attached together with Groovy config.

Here is the Groovy script using GCommons library that uses Logback: http://goo.gl/wuU05
Here is the patch that is now part of GCommons to make Logback load the config: http://goo.gl/pvSzz