rsReportServerDatabaseError - Timeout or low disk condition within the database

Error: An error occurred within the report server database. This may be due to a connection failure, timeout or low disk condition within the database. (rsReportServerDatabaseError)"

While configuring Report Snapshot / Caching, we face above mentioned issue because of Role/Permission issue in SSRS. Reporting Services uses a predefined database role called RSExecRole to grant report server permissions to the report server database.

RSExecRole should exists in Master, MSDB, ReportServer & ReportServerTempDB. Try the below code, it may solve your issue.

USE master
GO
GRANT EXECUTE ON master.dbo.xp_sqlagent_notify TO RSExecRole
GO
GRANT EXECUTE ON master.dbo.xp_sqlagent_enum_jobs TO RSExecRole
GO
GRANT EXECUTE ON master.dbo.xp_sqlagent_is_starting TO RSExecRole
GO

USE msdb
GO
GRANT EXECUTE ON msdb.dbo.sp_help_category TO RSExecRole
GO
GRANT EXECUTE ON msdb.dbo.sp_add_category TO RSExecRole
GO
GRANT EXECUTE ON msdb.dbo.sp_add_job TO RSExecRole
GO
GRANT EXECUTE ON msdb.dbo.sp_add_jobserver TO RSExecRole
GO
GRANT EXECUTE ON msdb.dbo.sp_add_jobstep TO RSExecRole
GO
GRANT EXECUTE ON msdb.dbo.sp_add_jobschedule TO RSExecRole
GO
GRANT EXECUTE ON msdb.dbo.sp_help_job TO RSExecRole
GO
GRANT EXECUTE ON msdb.dbo.sp_delete_job TO RSExecRole
GO
GRANT EXECUTE ON msdb.dbo.sp_help_jobschedule TO RSExecRole
GO
GRANT EXECUTE ON msdb.dbo.sp_verify_job_identifiers TO RSExecRole
GO
GRANT SELECT ON msdb.dbo.sysjobs TO RSExecRole
GO
GRANT SELECT ON msdb.dbo.syscategories TO RSExecRole
GO