Problem: Report can not be found (Error: Report file does not exist)
Solution: If it's saying the report file doesn't exist, you are probably trying to run a report off the network and not the computer the service or scheduled task is running on. That's fine, but you must change the authentication for the service or scheduled task.
By default, a service or a scheduled task is run as "local service"; all services run that way. And security within Windows does NOT allow a service to access ANYTHING on the network. That's why it's saying report not found, because the service running the batch can't access that drive.
That said, if it's an Event Server batch that is not working, you can configure the Report Runner Event Server Service to "run as" your ID/password.
For configuring a scheduled batch, you can go into Report Runner Batch, open your Batch XML file, and select the Scheduler button to modify and/or add the scheduled task with this setting.