Create a Watch Rule fails on a numeric data item

Hello,

I am trying to create simple watch rules, so that users can be alerted if report comes back with value that is either too high or too low.

Following Cognos instructions:
1. Created simple report that contains simple 2 column table:
Geography|Age.
2. Set Age to be of a Number data format.
3. Grouped by Geography and set both aggregate functions of Age to Average.
4. Created an HTML version of this report.

Now when I right click on my Age column, I can see the option 'Alert Using New Watch rule...' However, when I click on it it comes back and says 'Invalid selection for creating a watch rule. '

Any ideas, comments and suggestions would be appreciated.

Thank you,

Nataliya