@Gareth hard to tell without more details, my guess is the Java version, we have recently increased the java version you need to build, specially with Lucee 6.1 you know need Java 21. I guess with Lucee 6.0 it has to be at least Java 11, but i’m not certain on that from top of my head.

thanks, I've gone back to 6.0.1 for now and clearing the workspace in my Jenkins setup fixed the issue