If a user changes their name, any previous meetings they have booked in resource central will not show up in their My Meetings view.
Therefore if a user wanted to make any changes this would not be possible.
To fix, the original meetings need to be re-associated with the new username. This can be done by running a query on the Resc_Central_RC database on the SQL server. This is the command
Update Reservations set OrganizerEmail = 'djeffrey@imgroup.co.uk' where organizeremail = 'dchambers@imgroup.co.uk'
Backup the database first just to be sure
