Hi Sanjay,
If you have not assigned the responsible agent in workflow task, in that case at run time all possible users will receive the work item.
If you have assigned a container in responsible agent but at run time it does have any value in it or it has wrong value in it, in that case no body will receive the work item.
Also, in case you have assigned a container in responsible agent, then make sure you concatenate 'US' with the user names or the other relevant prefixes based on what type of agents they are.
Richa
