error en modify !

[Karla V.]

Porque me da error este estupido modify??

loop at zTotal where alterna(5) = 'Total'.
cNomb = zTotal-alterna+6.
read table zCta_Ceco_S with key nivel3 = cNomb into wa.
wa-txt50 = 't'.
wa-inicial = ztotal-inicial.
wa-debe = ztotal-debe.
wa-haber = ztotal-haber.
wa-saldo = ztotal-saldo.
modify zCta_Ceco_S from wa." le puse un index sy-index y nada
endloop.