In special cases, it may happen that tabs and icons in the version 6.0 user interface (CMS Desk, Site Manager) are duplicated. For example if you import an older site to version 6.0 or if the upgrade procedure was not followed properly during previous upgrades.
If this happens, UI elements stored in the CMS_UIElement table are created twice and displayed in the UI. To fix this issue you can apply the latest hotfix for version 6 or you can delete the elements which are duplicated by this script: RemoveDoubledUIElements.sql
The 6.0 elements have a unique ID, and the script attached will delete all elements which should not be there. As always, do not forget to create a database backup to be able to restore it if needed.