please tell me what is the reason behand dump here

hi,

am getting bump here..plz find the reason

loop at lt_incds where zappdat = lt_delivery-zappdat.

at end of zzacommcd.

sum.

lv_cnt = lv_cnt + 1.

gv_total_qty_del = gv_total_qty_del + lt_incds-zmeng.

if lv_cnt > 4.

lv_cnt = 1.

endif.

Note : at SUM am getting dump