We have 10 reports with data driven subscriptions which run each day on a
shared schedule (to create cached reports). Each report query (all stored
procedures) will run several times during this schedule for various parameter
combinations, a total of 78 queries.
We have experienced problems where this job takes several hours (rather than
several minutes) to complete, (I have not established the reason for this
yet), and then the Reporting Services service has shut down.
The application log shows: Report Server (MSSQLSERVER) cannot connect to the
report server database.

Why would this happen?