Hi Alberto,
As you said as you can see at communication str, just go to change mode at LBWE, click maintenance, select MCVBUK-FKSTK and move to extract structure(right --> Left side),save,continue.(Go to RSA6) double click on 2LIS_12_VCHDR,if Field FKTSK was hidden then un select hide column and save it.
you can check records at RSA3 after filling the setup tables.
Before filling setup tables always delete it Tx - LBWG.
Thanks