Summary columns in crosstabs

[thrishul]

Hi,
I need to add 2 summary columns to the end of my report.
One's a Total column the other an Average column of sales for each month of the year.

I need the Total & Average columns to be side by side in my cross tab.
Cognos Report Studio allows me to add only one summary column
(My selcection: choose the measure item then select Data -> Total)
I get the following message when I try to add the 2nd in the same way
(My selection: choose the measure item then select Data -> Average).

"No summarizable items could be implicitly determined. You can explicitly summarize an item by selecting an item on the edge and then summarizing."

Thanks in Advance