Why am I not able to create a new virtual disk?

In some situations you will not be able to create a new virtual disk to use in a virtual disk copy.

A virtual disk can be used as a target virtual disk in only one virtual disk copy at a time.
The maximum allowable number of virtual disk copies per storage array is dependent upon the number of target virtual disks available on your storage array.
A storage array can have up to eight virtual disk copies running at any given time.
The target virtual disk capacity must be equal to or greater than the source virtual disk capacity.