Symptoms
The case is User A set out of office and choose redirect to User B.
User B can see the task of User A but when User B open the task.
He will get error on "Worklist item could not be open. User B is not allow to open the worklist item"
The setting and error message was attached.
Diagnoses
On a worklist control, when the forwarded user clicks on the item to open the form, he receives a “Worklist item could not be opened” error. However, the same does not apply when the item is opened through Workspace.
Resolution
This is a known issue and our labs was able to provide a coldfix