Assign Type conflict with field symbols

Question

I have two tables tab1 & tab2, want to assign field values from tab1 to tab2 suing field symbols. Deatils are :
TYPES: BEGIN OF ty_tab1,
    item1   TYPE char20,
    item2   TYPE char20,
    val1 type i,
    val2 type i,
END OF ty_tab1,
BEGIN OF ty_tab2,
    item1 TYPE char20,
    item2 TYPE char20,
END OF ty_tab2.
DATA: it_tab1 TYPE TABLE OF ty_tab1,
            it_tab2 TYPE TABLE OF ty_tab2.
  FIELD-SYMBOLS <fs_tab1> TYPE ty_tab1.
                 <fs_tab2t> type ty_tab2.
  LOOP AT it_tab1 assigning <fs_tab1>.
    READ TABLE it_tab2  assigning <fs_tab2> WITH KEY item1 = <fs_tab1>-item1
                                                                                item2 = <fs_tab1>-item2.
    IF sy-subrc EQ 0.
      ASSIGN COMPONENT 'ITEM1' OF STRUCTURE <fs_tab1> TO <fs_tab2>.
     ASSIGN COMPONENT 'ITEM2' OF STRUCTURE <fs_tab1> TO <fs_tab2>.
    endif.
endloop.
Getting error msg
You attempted to assign a field to a typed field symbol, but the field does not have the required type.         
whats the reason of error.
Edited by: Matt on May 27, 2011 8:59 AM - added  tags

Answer 1

Taken from example dump
A new value is to be assigned to the field "...", although this field is
entirely or partly protected against changes.
The following are protected against changes:
- Character literals or numeric literals
- Constants (CONSTANTS)
- Parameters of the category IMPORTING REFERENCE for functions and
methods
- Untyped field symbols not yet assigned a field using ASSIGN
- TABLES parameters if the actual parameter is protected against changes
- USING reference parameters and CHANGING parameters for FORMs, if the
actual parameter is protected against changes and
- Accesses using field symbols if the field assigned using ASSIGN is
protected (or partially protected, e.g. key components of an internal
table with the type SORTED or HASHED TABLE) against changes
- Accesses using references, if the field bound to the reference is
protected (or partially protected) against changes
- External write accesses to READ-ONLY attributes,
- Content of a shared object area instance accessed using a shared lock
(ATTACH_FOR_READ).
You likely fall in one of these cases. Check each and if still unsure please share your code so we can reproduce the error.
Regards
Marcin