Hi @bravenel, I managed to get the same error message, but probably for different reasons.
Starting RM gives the following error message:
Logs:
[app:9] 2019-05-04 11:34:51.436 am [error] groovy.lang.GroovyRuntimeException: Ambiguous method overloading for method java.util.LinkedHashMap#leftShift. Cannot resolve which method to invoke for [null] due to overlapping prototypes between: [interface java.util.Map] [interface java.util.Map$Entry] (mainPage)
I can edit the child rules, simply cannot start the parent RM app.
I tried to create a Custom Command that invokes the launchAppPackage command in @gavincampbell's Fully DTH ([RELEASE] Fully Kiosk Browser Controller) with 1 parameter (type: string, value: com.spotify.music). It failed, and I cannot start the RM app since then.
Did I do something wrong? 
Edit: fw version 2.0.9.133
