mx4j Issues Following Upgrade to 2.1.6

[Biscuit Ninja <ca...@biscuit.ninja>]

We run some checks from our Monitoring software that rely on mx4j.

The checks typically grab some xml via HTTP request and parse it. For 
example, CF Stats on 'MyKeySpace' and 'MyColumnFamily' are retrieved 
using:

http://cassandra001:8081/mbean?template=identity&objectname=org.apache.cassandra.db%3Atype%3DColumnFamilies%2Ckeyspace%3DMyKeySpace%2Ccolumnfamily%3DMyColumnFamily

Periodically these checks result in a "HTTP 500 internal server error". 
The HTML body returned is empty.

The check most affected is for a CF/Table that sees the most inserts and 
the issue (so far) seems much more prolific when we are under load.

Any suggestions on how we can either debug or resolve the problem? Is it 
possible to obtain more diagnostic info/logging from mx4j?

The Cassandra system.log contains nothing in regard to mx4j except that 
it's loaded on start-up.

Any suggestions gratefully received.
Thanks in advance.