Many people are interested in creating subscriptions to Report Builder reports. In SQL Server 2005 this is only possible if the reports can be run unattended by the server. If the report has any user-dependent behavior, then it can only be run live by a user. Unfortunately, enabling model item security on a report model causes all reports against that model to potentially have user-dependent behavior. Therefore, as of this writing you cannot create subscriptions against a model-based report when the model has model item security enabled. We expect to fix this in a future release (how soon has not been decided yet).