When I click on Start Advanced Workflow action I am getting following error message.
ERROR [org.alfresco.web.ui.common.Utils] Failed to get to do tasks: org.alfresco.service.namespace.NamespaceException: Namespace prefix wf is not mapped to a namespace URI.
Could you provide us with - all your XML model and definition files, as customModel.xml - all your XML context files, as custom-model-context.xml and tell us where (in your filesystem) you put them.
Indeed, the problem is that the model that defines the "wf" prefix is not loaded at bootstrap