sql server job agent failed

Hello friends,

I have a task which runs at 8:00 pm every day....everyday it ran well, but yesterday and today the job failed and gave this error.

error Message:

Executed as user: NT Service\SQLSERVERAGENT. Microsoft (R) SQL Server Execute Package Utility  Version 11.0.2100.60 for 32-bit  Copyright (C) Microsoft Corporation. All rights reserved.    Started:  10:18:57  Error: 2015-08-18 10:19:13.04     Code: 0xC0016016     Source: DDDRetail Import SSIS      Description: Failed to decrypt protected XML node "DTS:Property" with error 0x8009000B "Key not valid for use in specified state.". You may not be authorized to access this information. This error occurs when there is a cryptographic error. Verify that the correct key is available.  End Error  Error: 2015-08-18 10:24:46.52     Code: 0xC0029183     Source: Remove Trans File from FTP FTP Task     Description: File represented by "/kde_0155/trans.txt" does not exist.  End Error  DTExec: The package execution returned DTSER_FAILURE (1).  Started:  10:18:57  Finished: 10:24:47  Elapsed:  350.612 seconds.  The package execution failed.  The step failed.

Please help me out with the solution.

Thanks 

Ranjan DS