Clone feature

I have tried to clone a KVM Windows XP VM. When I do try, I get the following error:

Full clone feature is not available at /usr/share/perl5/PVE/API2/Qemu.pm line 2093. (500)

There's lots of space on the storage that I want to create the clone on. There would not be enough storage on local storage, but the VM itself and the clone are on a separate hard disc.

What is the cause of this?