Cloning of running virtual machines is made possible by snapshots. The virtual machine is snapshotted and continues to run during the clone operation, freeing up the base disks to be copied for cloning. After the clone is complete, the snapshots are deleted.
However, snapshots cannot be taken of a virtual machine's independent disks. If a live clone operation is initiated, reading of the first independent disk after the snapshot process produces the error (followed by the datastore and the path the first independent disk).
For example:
A file was not found <datastore> <path to first independent disk>
Cloning of powered on virtual machines with independent disk(s) attached is not possible.
You must power off the virtual machine, then proceed with the clone operation.
Workaround:
To clone a VM while excluding any independent disks, during the clone wizard at the "Select Clone Options" section, check the box for "Customize this virtual machine's hardware." In the "customize hardware" section, deselect and remove any disks you wish to exclude in the clone operation.