Hi Renato,
The Transportation Cockpit is a special case in TM, and some generally valid concepts from the enhancement guide do not apply entirely.
Its appearance is controlled by the so called Page Layouts, which dynamically modify the layout.
There are two particular areas of interest:
(1) the OVP is completely built dynamically, so every customisation of the floorplan configuration /SCMTMS/WDCC_PLN is discarded.
(2) for some list, including the one where you have problems, the visibility of the buttons too is controlled by the page layouts.
For you situation, I suggest you to set a BP in the method /BOFU/IF_FBI_VIEW_EXITINTF_RUN~ADAPT_ACTION_PROPERTIES of class /SCMTMS/CL_UI_VIEWEXIT_PLN and check the "visible" and "enabled" property of your button in the parameter CT_ACTION_USAGE. If the button is deactivated at this point, you can add a POST exit to the said method and "correct" the properties.
The program will stop at that BP more than once (since that class runs for most lists from cockpit) - check out the attribute mv_list_object - for the list of freight units it should have the value 01.
Regards,
Dragos