"Operating system error 1394" - How can I prevent it?

I get occasional and random failures of my SQL Server backups with the error message Operating system error 1394

Does anyone know why this error occurs and how I can prevent it?

A little Googling tells me: http://msdn.microsoft.com/en-us/library/windows/desktop/ms681385%28v=vs.85%29.aspx

ERROR_NO_USER_SESSION_KEY
1394 (0x572)
There is no user session key for the specified logon session.

Which is great... but does not tell me WHY this happens.

The SQL server backs up to a remote Windows network share on an Windows 2008 Server. We run Active Directory. There is a whole fleet of 50+ SQL Servers of different versions (2000,2005,2008,2008R2), running on Windows 2003, 2008 and 2008R2 (Note to self: I really need to standardise!)

Running the backup again does not reproduce the error.

Full error message (redacted)

Microsoft.SqlServer.Management.Smo.FailedOperationException: Backup failed for Server 'SQLSERVER'.
  ---> Microsoft.SqlServer.Management.Common.ExecutionFailureException: An exception occurred while executing a Transact-SQL statement or batch.
  ---> System.Data.SqlClient.SqlException: Cannot open backup device '\\BACKUPSERVER\backups\SQLSERVER\DATABASE_NAME\TRANSACTIONLOG_backup_20111118_104731.trnz'. Operating system error 1394(failed to retrieve text for this error. Reason: 15105).
BACKUP LOG is terminating abnormally.
   at Microsoft.SqlServer.Management.Common.ConnectionManager.ExecuteTSql(ExecuteTSqlAction action, Object execObject, DataSet fillDataSet, Boolean catchException)
   at Microsoft.SqlServer.Management.Common.ServerConnection.ExecuteNonQuery(String sqlCommand, ExecutionTypes executionType)
   --- End of inner exception stack trace ---
   at Microsoft.SqlServer.Management.Common.ServerConnection.ExecuteNonQuery(String sqlCommand, ExecutionTypes executionType)
   at Microsoft.SqlServer.Management.Common.ServerConnection.ExecuteNonQuery(StringCollection sqlCommands, ExecutionTypes executionType)
   at Microsoft.SqlServer.Management.Smo.ExecutionManager.ExecuteNonQuery(StringCollection queries)
   at Microsoft.SqlServer.Management.Smo.BackupRestoreBase.ExecuteSql(Server server, StringCollection queries)
   at Microsoft.SqlServer.Management.Smo.Backup.SqlBackup(Server srv)
   --- End of inner exception stack trace ---
   at Microsoft.SqlServer.Management.Smo.Backup.SqlBackup(Server srv)
   at SqlBackup(Object , Object[] )
   at System.Management.Automation.DotNetAdapter.AuxiliaryMethodInvoke(Object target, Object[] arguments, MethodInformation methodInformation, Object[] originalArguments).InnerException.message