It's been years since this post but since I recently got into the same issue and here is why:
linked clones VM are useful to save storage space in case you deploy a lot of VMs all based on the same template and few modifications afterwards.
You save space by reusing the vmdk files of the original VM, and adding individual vmdks to store the differences.
This however implies that the original and the clones all need to be on the same datastore or datastore cluster.
In CLPEDUC's case, adding "Template" to the datastore cluster puts original vmdks and cloned into the same storage cluster and all is well.
Take Template out of the lcuster, and the original vmdk files cannot be "seen" in the destination datastore (cluster) hence, the incompatibility.
Resolution:
a - don't use linked clones, use plain clone.
b - if you want to take advantage of linked clones, clone and starting vm must reside on the same datastore (cluster).