Unable to deploy OVF-Template from URL (error 503 server unavailable)

Hi,

I'm trying to deploy an OVF-Template following this instructions:

http://www.lazywinadmin.com/2013/03/how-to-deploy-ovf-template-from-remote.html

The OVF-Template is located on a datastore on the same ESXi where I need to deploy it.

The Deploy-OVF-Template Dialog is able to read the OVF-Descriptor as the VMs Name, size, networks etc. are recognized correctly. But when the import starts It instantly runs into:

Failed to deploy

Unable to access file:

https://<ESXI-IP>/folder/<VM>/<VM>-disk1.vmdk

The remote server returned an error: (503) server unavailable

httpClient is already enabled in the ESXi's firewall.

Any help appreciated.