Windows 7 environment, running Outlook 2010 with Exchange 2010:
User's boss has shared his task list with her. She can add, delete, and edit tasks in her own task list with no problem. When she goes to add, delete, or edit a task in his tasks though, Outlook closes out. I have checked the event logs and I don't see any entries from Outlook when this happens.
She CAN, however, edit his tasks in-line from the list view by clicking in the desired field and editing.
The only possible fix that I can find is to set compatibility mode to Windows XP SP3. When I did this, she couldn't even launch Outlook: not able to load default folders.