The Jenkins controller was restarted while the build was running a step which cannot be resumed. Some steps like sh or input are written to survive a Jenkins restart and simply pick up where they left off when the build resumes. Others like checkout or junit normally complete promptly but cannot tolerate a restart. In case one of these steps happened to be in progress when Jenkins shut down, the resumed build will throw an error; using this condition with retry allows the step (or the whole enclosing node block) to be rerun.