minor update to error reporting
minor update to error reporting

adamallo/beast-mcmc,beast-dev/beast-mcmc,4ment/beast-mcmc,4ment/beast-mcmc,adamallo/beast-mcmc,beast-dev/beast-mcmc,beast-dev/beast-mcmc,adamallo/beast-mcmc,adamallo/beast-mcmc,adamallo/beast-mcmc,4ment/beast-mcmc,adamallo/beast-mcmc,beast-dev/beast-mcmc,4ment/beast-mcmc,4ment/beast-mcmc,4ment/beast-mcmc,beast-dev/beast-mcmc,beast-dev/beast-mcmc