Call to FireEventAction getting accessdeniedexception

Any idea what causes the error of Access denied? In the code I try to run rs.Fireevent(TimeSubscription,SubscriptionID) but I'm getting error below that shows in the SSRS log. I'm using service account that has access to subscription, I also created the subscription using the Service Account. I also given the Service acct db_owner access to ReportServerDB and ReportServerDBTemp. My last option is to try the service account that is used in the SSRS configuration.

library!ReportServer_0-68!d10!08/31/2012-09:59:29:: Call to FireEventAction(TimeSubscription, 72eb31b6-6797-4ae9-b8f5-6b671fbf3b51, ).
library!ReportServer_0-68!d10!08/31/2012-09:59:29:: e ERROR: Throwing Microsoft.ReportingServices.Diagnostics.Utilities.AccessDeniedException: , Microsoft.ReportingServices.Diagnostics.Utilities.AccessDeniedException: The permissions granted to user 'Domain\ServiceAccount' are insufficient for performing this operation.;