Error while executing Function Module for Customized Delta Extraction

Hi,

I've created a Function Module For Customized Delta Extraction and which checking that I'm getting Following Error.

"Field "P_R_ERDAT" is unknown. It is neither in one of the specified tables nor defined by a "DATA" statement . . . . . . . . . ."

And for 'P_R_ERDAT', i wrote the following Code :

loop at i_t_select .

case i_t_select-fieldnm.

when 'ERDAT'.

move-corresponding i_t_select to p_r_ERDAT.

append p_r_ERDAT.

.....

....

..

endcase.

endloop.

.....

....

pen cursor with hold s_cursor for

select * from ZTABLE_11

where TMSTMP in l_r_tdldate

and ERFZEIT in l_r_erfzeit and

ERDAT in p_r_ERDAT and

..........................

....

..

Please Advise..

Regards,

Anuja