Unfortunately the full error is truncated from the message.
But as a start the SQL engine account needs access to the share its writing to, to perform the backup.
Check that W2K8SQL\SYSTEM have write access to \\W2K8SQLBACKUP\SQLBackup\wslogdb70_28
If you could get the full error out we should be able to see whats going on. This link may help http://www.sqlservercentral.com/articles/SQL+Server+Agent/67726/