Outlook Error- The task cannot be updated

hi,

I have recieved an error for some users where they try to edit the workflow task using outlook they recieve error - the task can not be accepted/updated. The users do have permissions on the sharepoint list and the workflow is running under system accont impersonation.

In workflow history it says :

Event type                     Description                                    Outcome

Task rolled back            Task update by _SP was rejected     Reason: The user who attempted to complete

the task is not the user to whom the task is assigned

The workflow is using two approval task, if one gets approve it goes to another but if it gets rejected then it stops the workflow. I want to understand why only certain users are affected.

thank you.

nish