Scenario: 

In the full access user able to “Export To”/”Email As” that Sales Invoice in Preview Mode

But customize access right user unable to “Export To”/”Email As” that Sales in Preview Mode

Solution:

Maintenance > User Roles > Select the user role that cannot “Export To”/”Email As” Sales Invoice > Go to Reports tab > Search for ‘Sales Invoice’ > Enable ‘Export’.

Kindly refer attachment for details