getting dump in my Z program

hi,

i am getting dump in my below code in the delete statement line.actually previously it worked fine but now suddenly we r getting dump in the second delete statement below.can some body tell me the reason.

error analysis: You attempted to change, delete or create a line in the

internal table "\PROG=YBDISEMAT\DATA=INT_MARC", but no valid cursor exists

for the table.

Possible reasons:

1. The relevant ABAP/4 statement does not include the addition

"...INDEX...", although the statement is not

inside a "LOOP...ENDLOOP" loop processing this table.

2. The relevant ABAP/4 statement was called from within a

"LOOP...ENDLOOP" loop after a DELETE "\PROG=YBDISEMAT\DATA=INT_MARC".

LOOP AT int_marc INTO wa_marc.

IF wa_marc-werks IN ra_source.

READ TABLE int_disgr WITH KEY zdisgr = wa_marc-disgr

zwerks = wa_marc-werks.

IF sy-subrc NE 0.

DELETE int_marc.

ENDIF.

ENDIF.

IF wa_marc-werks IN ra_zmdc.

READ TABLE int_disgr WITH KEY zdisgr = wa_marc-disgr

zwerks = wa_marc-werks.

IF sy-subrc NE 0.

DELETE int_marc. _______________________________________________ getting dump here

ENDIF.

ENDIF.

CLEAR wa_marc.

ENDLOOP.