I suspect one of your actors, or something it calls, is broken in the build. "Async Launch Shell" is what calls all the actors, and any one being broken will throw an error like this. What I would do to debug is build all my actors as separate EXEs. Even if they don't do anything when run by themselves they should at least run. See if you get an error in building one of them. Unfortunately, debugging EXE problems is very painful and time-consuming. You could try re-asking your question on the main "Messenger Library" thread, as other developers who use it on RT have posted there and may have advice.