Function module error

Hello,

I am having problems setting up function module to pass the calendar date to a field in a BPS planning folder.

Here is the code for the FM:

FUNCTION ZBPS_GET_CALDAY.
*"----------------------------------------------------------------------
*"*"Local Interface:
*" IMPORTING
*" REFERENCE(I_AREA) TYPE UPC_Y_AREA
*" REFERENCE(ITO_CHA) TYPE UPC_YTO_CHA
*" REFERENCE(ITO_SOURCE) TYPE UPC_YTO_CHA
*" REFERENCE(ITO_TARGET) TYPE UPC_YTO_CHA
*" CHANGING
*" REFERENCE(XS_CHAS) TYPE ANY
*" EXCEPTIONS
*" FAILED
*"----------------------------------------------------------------------
* Get calendar date and pass back to BPS app

FIELD-SYMBOLS: <calday>.

ASSIGN COMPONENT '0CALDAY' OF STRUCTURE XS_CHAS TO <calday>.

<calday> = sy-datum.

ENDFUNCTION.

When trying to execute the FM it abends with a MOVE_TO_LIT_NOTALLOWED_NODATA message.

Any assistance would be appreciated.

Thank you.