Job is not running but activity monitor is showing next schedule time

Hi,

My backup jobs are not running. activity monitor is showing next schedule time but job is not running & there is no any failure log or error i have found in sql server error log. but i have observed some errors in sql agent error log.

1. Failed to retrieve job 0xBF59BADA42EC234883D08C3A2007F742 from the server
2. Error: 229, EXECUTE permission denied on object 'sp_sqlagent_refresh_job', database 'msdb', schema 'dbo'. [SQLSTATE 42000]
3. Error: 229, UPDATE permission denied on object 'sysjobschedules', database 'msdb', schema 'dbo'. [SQLSTATE 42000] (SaveAllSchedules)

Please help me to sort out this.