When a user clicks a Request Review task link via the "My Workflow task" webpart page this opens the workflow task to be completed by the user. Once user approves the workflow task, there is a redirection to the "My Workflow Tasks" webpart page with the approved task still showing. When the task is clicked again an error message is displayed. 

The sequence of events are: 
1. The user clicks a task in the task list, and the tasks form appears on the screen. 
2. The user clicks on the OK button and leaves the form. 
3. A task that was completed, it remains in the task list. 
4. The task disappears after the page is refreshed. 

This is a SharePoint environmental issue where the user is redirected to the "My Workflow tasks" webpart page before workflow engine has completed updating the task outcome and task state. Therefore, the "My workflow tasks" webpart page will need to be manually refreshed to update the task list accordingly.