If an end user receives the message "You have insufficient rights to access object (CREmailActivityMaint)" when trying to email, then there's an issue with the role assigned to that user.
To resolve the issue, on the Access Rights By Role screen, within the hidden folder, you need to set the appropriate access rights to the row with the description Email Activity.
Go to the menu path Configuration > User Security > Manage > Access Rights By Role.
Select the role and go to the first hidden menu path in the left hand side of the screen.
Filter on the column description in the right hand side and filter on column header contains Email.
Once filtered, set the access rights to delete for the description which equals Email Activity.
Once this has been set, then the end user will not get the message about insufficient rights again.