iam not able to sum the amount field(SUM) in my ALV report

Dear Freinds,

I have create a custom report relatign to payroll. IN my ALV report iam getting

this message that ""

could any one please correct me in the field cat what exactly ihave to do.

i have used as follows . in different ways like below

ls_fieldcat-fieldname = 'SALARY'.

ls_fieldcat-seltext_l = 'Salary'.

ls_fieldcat-col_pos = 7.

ls_fieldcat-outputlen = 20.

ls_fieldcat-do_sum = 'X'.

• ls_fieldcat-ref_fieldname = 'WAERS'.

• ls_fieldcat-ref_tabname = 'T500C'.

• ls_fieldcat-datatype = 'CURR'. "CURR

ls_fieldcat-inttype = 'CURR'. "CURR

APPEND ls_fieldcat TO fp_i_fieldcat.

Iam getting this message to click total of salary on my alv ouput it is giving message as

" Desired operation cannot be performed for column 'Salary' "

Please let me know .....what i have to get the salary amount when i try to do sum.

Regards

Latha