The condition class
java-serious-exception is signaled for an exception that is serious, which means something in the system is not really not as it should be. Applications that get this should try to save everything and exit.
In general, these exceptions should not happen, and you should not need to worry about these. If you do get any such exception, please report it with as many details as possible to Lisp Support, following the guidelines at
LispWorks User Guide and Reference Manual - 20 Sep 2017