I have the same issue as Senthil, and I've looked at the content of C:\Alfresco\tomcat\webapps\alfresco\WEB-INF\classes\alfresco\web-client-config-actions.xml.
I was expecting to find an Action entry for the "Start Advanced Workflow" action… but this is totally missing from the config file (I'm working on 2.1.2 Enterprise). Am I doing something wrong?