我在 centos 上设置 mcollective activemq 设置时遇到以下错误，您能告诉我设置过程中出了什么问题吗？
mco ping
The ping application failed to run, use -v for full error details:
Could not create instance of plugin MCollective::Connector::Activemq: undefined method `str_to_bool' for MCollective::Util:Module
Ruby 版本：
ruby 1.9.3p429 (2013-05-15 revision 40747) [x86_64-linux]
客户端 cfg 文件：
#topicprefix = /topic/mcollective
main_collective = mcollective
collectives = mcollective
libdir = /usr/libexec/mcollective
#logger_type = console
logfile = /etc/mcollective/mco.log
loglevel = debug
# Plugins
securityprovider = psk
plugin.psk = unset
connector = activemq
plugin.stomp.pool.size = 2
plugin.stomp.pool.1.host = localhost
plugin.stomp.pool.1.port = 61613
plugin.stomp.pool.1.user = mcollective
plugin.stomp.pool.1.password = marionette
# Facts
factsource = yaml
plugin.yaml = /etc/mcollective/facts.yaml
问候，
萨蒂亚