the actual share will be \\W2K8SQLBACKUP\SQLBackup and not \\W2K8SQLBACKUP\SQLBackup\wslogdb70_28.
Check the permissions at the share level and also the NTFS permissions too on the subfolder wslogdb70_28.
Check the account that sql agent is running under and ensure that the correct access is granted
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"Ya can't make an omelette without breaking just a few eggs" 😉