Hi
You're using WA_MSEG2 as headerline while readinf IT_KNA1, you should use WA_KNA1:
read TABLE it_kna1 into wa_mseg2 with key kunnr = wa_mseg-kunnr.
read TABLE it_kna1 into wa_knawith key kunnr = wa_mseg-kunnr.
if sy-subrc = 0.
move wa_kna1-name1 to wa_mseg2-name1.
Max