Backups are intermittently failing with the above error. Symptoms include random failures on different virtual machines, particularly on a backup job where multiple virtual machines are being backed up.
It is possible that there is a storage issue in your environment. You can investigate if there is a storage performance issue by using ESXTOP. The following VMware knowledgebase article, desrcibes how to do this in detail: kb.vmware.com/kb/1008205
Lower the number of VMs being backed up at the same time. To do this navigate to vRanger GUI, then Tools | Options | My Jobs | Configuration.
In the Resource Management Window find the parameter 'Maximum number of tasks running locally (1 - 20)', decrement this value by 1 and run the job again. Keep lowering this value until the error has stopped. If this is the case, then a storage performance issue is at play here.