If you have created a roll-up summary field and it continues to display the spinning hour-glass icon, you may have advanced currency management enabled and be summarizing a currency field on the opportunity object.

If you have this feature enabled (you can check by going to Setup | Company Profile | Manage Currencies), you cannot create roll-up summary fields that calculate currency on the opportunity object. If you had set up any currency-related roll-up summary fields on the opportunity object, these will be disabled and their values will no longer be calculated.

Check the below link for more info

http://help.salesforce.com/HTViewSolution?id=000041377

Cheers!!!