You might run into this issue when running task processes in SharePoint Designer.
“Reason: The user who attempted to complete the task is not the user to whom the task is assigned.”
Assuming the person should actually be able to complete the task, check the following:
- Make sure the user who was assigned the task does not have multiple accounts. If they do, the task could have been assigned to the account that the person isn’t currently signed in as when attempting to complete the task.
- If it’s someone completing the task on behalf of another, make sure that individual is either:
- A Site Owner (site settings, site permissions, people and groups, site owners) or
- Task process owner (in SPD 2010 workflows, go to the properties for the task step and set task process owner. Click OK and republish workflow.):