Hi Jan
Check this code. - Just add the highlighted statement in REPORT keyword. (NO STANDARD PAGE HEADING)
REPORT ZT1 NO STANDARD PAGE HEADING.
DATA test TYPE c Value ' ' .
WRITE test AS CHECKBOX.
Write 'Hallo??'.
AT LINE-SELECTION.
READ Line 1 FIELD VALUE test.
If test = 'X' .
Write 'Hallo'.
Else.
Write 'Tschüss'.
ENDIF.