In a SharePoint integrated SQL Server Reporting Services environment, you find you can access a model, open Report Builder, drag an drop a few items. But when you attempt to actually run the report you're told the model cannot be found. What? But you were just using it!
The error looks like:
An error has occurred during report processing. (rsProcessingAborted)
To Fix:
In SQL Server Reporting Services Configuration, check the Unattended Execution Account.
Provide this account access to the SharePoint library hosting your Model.