Can't Add TrendLine to Bar Chart

[Casey]

Hi,

I am using Access '97. I can add trend lines to
some of my charts, but when trying to add one to a simple
bar chart which shows simple amounts per bar, I cannot.
The Add Trendline option is greyed out when I try to use
it with my bar chart. Is there something I can do. I
really would appreciate any help.

Thank you,

Casey