In excel 2007 I want to compare to series in bar graphs. I want to put error
bars on the graph. The series values are averages of multiple numbers and
standard deviations and standard errors of means are easily calculated. When
go to format selection, select my series and then click on the layout tab,
I see the "Error bars" control, but it is faded out as if it is inactive.

How do I activate this function so that I can add error bars to my graph?
Does the data have to be entered in a specific manner in order to generate
error bars?