If your campaign is a paid search campaign, you may have to wait a little while for cost data to be displayed for reasons outside of the control of Yahoo! Web Analytics. For example, you must wait 24 hours for Google Analytics data to be collected.
Are you sure you haven't missed anything?
- Check the set-up of your campaign at Settings > Campaigns & Ad Channel > Ad Channel Configuration. Have you spelled everything correctly? Have you ensured that this is how your campaign should be identified?
- Have you tested the campaign? Click on the ad / banner / link which brings a campaign visitor to your site. Now look at the Campaign Summary report at Reports > Marketing > Campaigns > Campaign Summary.