I encountered the same issue, but later discovered it had to do with the audit trail log directory. When I had the audit trail log directory set to /var/log/jenkins/audit-%g.log, I got that error. Then I changed it to /var/jenkins_home/logs/audit-%g.log, it worked. The default jenkins log dir of my installation is /var/jenkins_home/logs. 

Hope this helps. 

After further testing, it appears that the initial configuration of this plugin does not work (I deployed Jenkins using a helm chart, so the plugin was configured as code). After the deployment, I am getting the same error when performing some action that would trigger the plugin to create a log file. Then, I went into the Jenkins Configure System UI and manually update one of the values in the plugin configuration, say, Log File Size, save the configuration, then the error goes away, and the plugin started working correctly. This behavior is consistently repeatable. 

Might be something to fix in there: https://github.com/jenkinsci/audit-trail-plugin/blob/master/src/main/java/hudson/plugins/audit_trail/AuditTrailPlugin.java#L65-L84

Apologies, I missed the bug report, somehow the plugin default assignee wasn't changed on plugin ownership transfer.

Regarding the reported issue, it appears that the path you are specifying doesn't exist on the host and the FileHandler used by the plugin is not able to create the intermediate missing directories. I'll make a fix for this, in the meantime, workaround is to manually create the intermediate directories.

After further testing, it appears that the initial configuration of this plugin does not work (I deployed Jenkins using a helm chart, so the plugin was configured as code). After the deployment, I am getting the same error when performing some action that would trigger the plugin to create a log file. Then, I went into the Jenkins Configure System UI and manually update one of the values in the plugin configuration, say, Log File Size, save the configuration, then the error goes away, and the plugin started working correctly

qisylvia this description makes me think that you are describing a different issue, with an incompatibility between the jcasc plugin in the audit trail plugin. I can see that you logged JENKINS-57232 that seems to cover the issue, I propose to discuss this specific issue in there and keep JENKINS-56108 for the issue reported initially.