I thought I would throw this out to the list before I started deep diving. I'm logging with org.slf4j.Logger and logback classic in an app running in Tomcat. Tomcat is using its regular JULI logging. When I use: logger.error(msg); Everything works great. But when I add a Throwable in there: logger.error(msg, t); The connection thread hangs in tomcat. Just thought I'd see if anyone has run into this before. M