SUM ROWS HORIZONTALLY IN RDLC REPORT

HELLO,

I am totally confuse how to solve this.

i have a RLDC report with tablix and some columns:

column1      column2       TOTAL

100              150             #Error

250              100

NOW i want the total of column1 and column2 should show in TOTAL.

i used different Expression like this

=sum(Fields!column1.value + Fields!columns2.value)

=sum(Fields!column1.value) + Sum(Fields!columns2.value)

and some more but not succeeded its Showing #Error in Report Priview.

Any Expert having time, Please HELP ME.

its very urgent.