error -not mutually convertible in a Unicode program

Hi all,

I have declare my internal table and workarea as below ...

TYPES: BEGIN OF t_mara,

matnr type mara-matnr,

END OF t_mara.

DATA : it_mara TYPE t_mara OCCURS 0 WITH HEADER LINE.

DATA :wa_mara like mara-matnr.

when iam loopimg my internal table into work area(like loop at it_mara into wa_mara ......) .. iam getting below error

A line of "IT_mara" and "wa_mara" are not mutually convertible in a Unicode program. Unicode program.

Can any one let me know what is the exact problem ?..

Thanks

MAHA