Failed backup

Hi All,
can someone help me with this issue. My nightly full backup job is failing with this error

Executed as user: NT SERVICE\SQLSERVERAGENT. Warning: Null value is eliminated by an aggregate or other SET operation. [SQLSTATE 01003] (Message 8153) Backup database: master MgmtClass: 21Day [SQLSTATE 01000] (Message 0) Processed 520 pages for database 'master', file 'master' on file 1. [SQLSTATE 01000] (Message 4035) Processed 2 pages for database 'master', file 'mastlog' on file 1. [SQLSTATE 01000] (Message 4035) BACKUP DATABASE successfully processed 522 pages in 0.084 seconds (48.543 MB/sec). [SQLSTATE 01000] (Message 3014) Backup database: model MgmtClass: 21Day [SQLSTATE 01000] (Message 0) Processed 344 pages for database 'model', file 'modeldev' on file 1. [SQLSTATE 01000] (Message 4035) Processed 2 pages for database 'model', file 'modellog' on file 1. [SQLSTATE 01000] (Message 4035) BACKUP DATABASE successfully processed 346 pages in 0.038 seconds (70.942 MB/sec). [SQLSTATE 01000] (Message 3014) Backup database: msdb MgmtClass: 21Day [SQLSTATE 01000] (Message 0) Processed 8232 pages for database 'msdb', file 'MSDBData' on file 1. [SQLSTATE 01000] (Message 4035) Processed 3 pages for database 'msdb', file 'MSDBLog' on file 1. [SQLSTATE 01000] (Message 4035)
One or more backups failed. See database-level errors for details. [SQLSTATE 42000] (Error 50000) BACKUP DATABASE successfully processed 8235 pages in 0.577 seconds (111.498 MB/sec). [SQLSTATE 01000] (Error 3014) Backup database: MgmtClass: 21Day [SQLSTATE 01000] (Error 0) Backup database: IMG MgmtClass: 21Day [SQLSTATE 01000] (Error 0). The step failed.