User A was in the organization.  User B is a new user.  User B took over User A's role.  I originally renamed User A to User B, but decided to create a new account and import User A's pst into User B's mailbox.  Deleted User A's account.  

When User B modifies a calendar entry that was originally created by User A, they are able to send updates, but receive a NDR stating they do not have permission to send on behalf as.  

Is there a way to give user B send as rights to a deleted account.  Or take full ownership of the calendar entries. Or clean up the references to User A in these entries.  I have seen posts on how to delete them, but the User B will need these for day to day operation.

Consider creating service mailboxes for roles and assigning the users rights on those roles.  Then it's really easy to reassign the role by changing rights.

The problem you are experiencing is normal.  You can't do what you did the way you did it.

Thanks, 

I figured as much.