Problem uploading VMware OS image using Sunstone

I’m trying to add a new image in Sunstone of type OS by pointing to the file location. The interface reports that the image was created successfully but no new image appears in the inventory.
The OS is a VMWare Server 2012 R2 OS and has just one disk/vmdk file. I have looked at the documentation but I am still unsure of what format I need to prepare the VM in and at what path the image ultimately resides. Do I point Sunstone at a folder conatining just the vmdk file and remove everything else (vmx file etc) from that folder? Do I need to zip the vmdk file and if so is tar.gz the only format that works, or does .zip work also? Where (at what path) are images stored once they have been successfully created? Sorry for all the questions but I am new to Sunstone and worth pointing out that i am a Windows head and am not very knowledgeable on Linux.

You need to create a folder and place the .vmdk file (nothing else) inside. You then need to create a tar.gz file from that folder, and create the image from that file.

They are placed in the images datastore, that should correspond to a ESX datastore, as per the following guide:

The VMFS Datastore — OpenNebula 4.12.1 documentation