Hi,
Change the below highlighted work area as same structure as it_kna1.
read TABLE it_kna1 into wa_mseg2with key kunnr = wa_mseg-kunnr.
if sy-subrc = 0.
move wa_kna1-name1 to wa_mseg2-name1.
replace as below.
read TABLE it_kna1 into wa_kna1with key kunnr = wa_mseg-kunnr.
if sy-subrc = 0.
move wa_kna1-name1 to wa_mseg2-name1.
Regards,
Pavan