Backup SQL Server failed -> Reporting Services restart

Hello everyone,

since a long time I have been experiencing a problem with SQL Server and Reporting Services I will now to explain.
I am using a Job in order to make a transaction backup every 20 minutes, but sometimes for no apparent reason the job begins to fail and throw the following error:

Executed as user: domain\user. BACKUP LOG is terminating abnormally. [SQLSTATE 42000] (Error 3013).  The step failed.

Please find the TSQL code for this step below:

BACKUP LOG [Database]
        TO DISK ='\\......\db_BackupTransaction_SQL.bak'
        WITH STATS = 1,
        NAME = 'db_BackupTransaction_SQL',
        DESCRIPTION = 'Transaction Backup with SQL Server',
        NOINIT,
        STOP_ON_ERROR,
        COMPRESSION

I have the same problem with different versions of SQL Server (since 2008), different Servers and differents Databases.

To eliminate the problem I am forced to restart Reporting Services. The questions are: why?, how can I solve this problem?, is it a bug from SQL Server/Reporting Services? Any similar experience?

Thanks in advance,