Subscription with a Prompt is Not Sent and Disappears

If you use a prompt on a report, and that prompt requires an answer but no default answer is provided in the prompt's design, and then that report is subscribed to, the subscription cannot execute the report successfully because the prompt requires an answer. The subscription is therefore invalidated and automatically removed from Developer's Subscriptions list.

For the subscription to work, you can redesign the prompt so that it has a default answer, or remove the prompt from the report.