Hi! I did not run into this specific problem, but I have had issues with class loaders, which made me write some very minimal code to respond to MIDI events coming from MMJ using just standard Java classes, and then delegate them to other threads running in Clojure which have access to the full Clojure class path. I wonder if you are running into something similar? If you can give me more details about how you have installed MMJ, and exactly what is failing (with stack traces, etc.) I might be able to help you debug it.