Hi, We have multiple production processes that run 24 hours a day, 7 days a week. All use slf4j/logback and recently we had several of these (seemingly coincidentally) spew: java.lang.NoClassDefFoundError: ch/qos/logback/classic/spi/ThrowableProxy These are long running processes where nothing has changed recently. Obviously the logback jars are available, in the right place, etc. I'm stumped. There are some hints of some possible system related problem (like missing NFS mount, possibly). Does logback dynamically load the above class? Again, this error is out of the blue, from a process that may have been running for days or weeks. Any ideas? We're using version logback 1.0.13. If I google the above, there are some references to "Spring Boot" which we are not using. However, we are using Spring Integration, in case that matters. Any ideas? Thanks, Fred