Description of Problem:
When "update respondent status" is chosen it claims "Attendee status can
not be updated because the item no longer exists".


Steps to reproduce the problem:
1. Create a task
2. Assign the task to another user (selected from an LDAP addressbook in
this case) 
3. The other user accepts the task, which sends a message back
4. Open the "Accepted:" message
5. Click "Ok" to update the respondent status

Actual Results:
Attendee status can not be updates because the item no longer exists

Expected Results:
Update the attendee status for the task to show "Accepted"

How often does this happen? 
Always.