Sum total of report column

Question

I try to sum the total of a column of my report based on =ReportItems!Textbox135.Value

This field is not included in the dataset, but is a textfield in the report. I use the following expression in the group header of my report

=SUM(ReportItems!Textbox135.Value)

Which results in the error:

Aggregate functions can be used only on report items contained in page headers and footers

What is the correct expression to sum report items?

Answer 1

Have you tried:

=SUM(Fields!YourField.Value)