Could you try to add the user
bn_jasperserver to the database
To get the password of the user
bn_jasperserver of the application
installdir/apps/jasperserver/buildomatic/build_conf/default/js.jdbc.properties you need to update this in the next command.
mysql -u root -p -e grant all privileges on DATABASE_NAME.* TO 'bn_jasperserver'@'localhost' identified by 'PASSWORD';
But maybe this doesn't work, we think there was an error in the installation so we recommend you to reinstall JasperReports
If you still have the same error, you could pass us the installation logs that are in