IF ALEN(aDV, 1) = 0
    FOR nIdx = 1 TO nCFldCnt
        nField = cCFlds[nIdx]
        IF aDV[nField]==["]  && wgcs
            * Remove surrounding quotes

            aDV[nField] = SUBSTR( aDV[nField], 2, LEN(aDV[nField])-2 )  && wgcs
        ENDIF
    ENDFOR
ENDIF

You're retrieving value nField from array cCFlds (the value I presume is numeric) -- are you absolutely sure that the value you're obtaining isn't less than 1 or is greater than the size of the array aDV ?