just forgot this lines

catalog/admin/includes/boxes/customers.php

< -- FIND -- >

'' . BOX_CUSTOMERS_CUSTOMERS . '
' .

< -- ADD AFTER IT -- >

'' . BOX_PRIVATE_MESSAGES . '
' .

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catalog/admin/includes/languages/english.php

--ADD THIS TO THE BOTTOM OF THE FILE (before '?>')--

define('BOX_PRIVATE_MESSAGES', 'Private Messages - Admin');

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this is a full pack with the fix

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