error message Backup exec server

I'm getting the following error message on the backup exec server every 5 minutes.  
(in the Event viewer  the level is information)

Apparently all is fine but I would like to know what the problem exactly is .
Thank you

We use backup exec 12 version 14.2 rev.1180 (64 bit)

Log Name:      Application
Source:        MSSQL$BKUPEXEC
Date:          9/30/2015 1:54:42 PM
Event ID:      18456
Task Category: Logon
Level:         Information
Keywords:      Classic,Audit Failure
User:          contoso\dom-backupadmin
Computer:      hq99.contoso.ORG
Login failed for user 'contoso\dom-backupadmin'. Reason: Failed to open the explicitly specified database. [CLIENT:]
Event Xml:
<Event xmlns="">
    <Provider Name="MSSQL$BKUPEXEC" />
    <EventID Qualifiers="49152">18456</EventID>
    <TimeCreated SystemTime="2015-09-30T11:54:42.000Z" />
    <Security UserID="S-1-5-21-1606980848-162531612-839522115-28608" />
    <Data> Reason: Failed to open the explicitly specified database.</Data>
    <Data> [CLIENT:]</Data>
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Vitor MontalvãoMSSQL Senior EngineerCommented:
Looks like contoso\dom-backupadmin doesn't have backup rights on the SQL Server instance.

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CarloAuthor Commented:
you are right ..... Symantec sent me this link . this is probably due to an upgrade and a domain migration on that machine.

here is the article.
SQL Event 18456 during file backup of SQL server:
Please find the Tech article:
CarloAuthor Commented:
solution found
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