Exception message "Incompatible object argument for function call" with a nasty long stack trace, and it seems so generic that you may never find the answer.

What this almost always means to me, and what I almost always forget, is a library (dependency) version mismatch or more commonly that I've shoved a development version of a JAR into my applications lib/ directory to perform diagnostics and then subsequently updated the application - typically through a mechanism like an RPM installed by yum - where the development version of the JAR is still present in the classpath. Obviously this becomes a problem with wildcard classpath convenience, but easy to diagnose and fix, as long as it can be remembered. Or optionally perform some sort of cleanup in the %%postun in RPM for the lib/ directory, which is what I think I'll impose.