VMware vSphere 4 SAN storage with multiple data-stores No vCenter

I shut-down a virtual machine and using the data-store browser did a copy/paste to copy the VM to a new datastore with additional space. The file copy performance was very poor, and due to time constraints I decided to cancel the copy task. However the copy task showing in the vsphere client can not be cancelled; the cancel option is disabled.

Currently I am not able to start the machine in it's original location as the disk files are locked for the copy. How can I abort the copy? I tried deleting the target directory but this did not abort the copy task.