In case you want to use the taskmanager feature in Content Navigator with CM8 users it is required that you deploy the CMContainerLogonPlugin.jar in your Content Navigator. This is required for the password decryption between WebSphere/LDAP users and Content Manager users is working. The plugin must be requested by the IBM support as this is not part of the default Content Navigator deployment.
It is also mandatory that the password of the WebSphere/LDAP users are identical to the CM8 users.