Backup failing with "2212 - Unknown error" (4033106)

Backing up a VMware virtual machines fails with the following error:

Error: 2212 - [vix_cant_read_detail] VIX can't read [Datastore] VirtualMachine.vmdk (Unknown error) [at vddkd_read:717]

There can be several reasons for this specific error. The following are the most common causes:

• VMDK corruption.
• Datastore disconnections or I/O read errors. 
• The management agent is not working correctly. 

This issue may potentially affect all the virtual machines in a datastore or all machines in a host. Since it can also affect one particular virtual machine, the following approach is recommended:

1. Restart the vRanger services.
2. Perform a vMotion of the affected virtual machine to a different host. 
3. Perform a Storage vMotion of the affected virtual machine to a different datastore.
4. Restart the ESXi management agents. You can follow VMware KB1003490 for further instructions regarding this step. 
5. Restart the vCenter server.

If the problem continues, please open a support case and provide the relevant logs along with the Virtual Center support bundle.