SQL Job continues to Fail

Windows 2008 R2 64 Bit server
SQL 2008 64 bit

This is a daily transaction log backup the was running for several months now all of a sudden it has been failing.  I run this six days a week and do a full backup on Sunday.
The full backup works everytime

Below are the errors



Type :            Error
Date :            2/18/2013
Time :            12:15:01 AM
Event :            3041
Source :            MSSQLSERVER
Category :      Backup
User :            MY\\sqlagent
Computer :      server10.my.network.mydomain.com
Description:
BACKUP failed to complete the command BACKUP LOG SUSDB. Check the backup application log for detailed messages.

Type :            Error
Date :            2/18/2013
Time :            12:15:02 AM
Event :            12291
Source :            SQLISPackage100
Category :      None
User :            OUR\sqlagent
Computer :      server10.my.network.mydomain.com
Description:
Package "DB Maintenance Plan SUSDB" failed.

Type :            Warning
Date :            2/18/2013
Time :            12:15:03 AM
Event :            208
Source :            SQLSERVERAGENT
Category :      Job Engine
User :            N/A
Computer :      server10.my.network.mydomain.com
Description:
SQL Server Scheduled Job 'DB Maintenance Plan SUSDB.Subplan_5' (0x424DE5598E62D64F9DC325BE113AD634) - Status: Failed - Invoked on: 2013-02-18 00:15:00 - Message: The job failed.  The Job was invoked by Schedule 46 (DB Maintenance Plan SUSDB.Subplan_5).  The last step to run was step 1 (Subplan_5).



Any ideas