How to Achieve  the creation  of  activity records for each marketing list member  on Addition of marketing list to campaign in MSCRM  2011 Custom workflow:

1. First we have to create a text field ( to have latest marketing list guid which is associated recently ) which should be hidden on campaign  

2.  Update this field on  association of marketing list to campaign (Additem  plugin Message on campaign entity).

3. Write custom work flow on update of this campaign record hidden field   which will fetch the associated marketing list from campaign record based on  hidden field text (which is recently added marketing list guid) , then list members and create custom record for each.