Just managed to make it work!
What I did different now is:
* Uncompressed the image using linux command line (throught the Rescue CD prompt). First time I had done with WinZip, in Windows.
* Comparing my partitions to the ones you posted, I noticed that I had an "alert" icon in the SWAP and EXT4 and you didn't have it. So, after restorning the image, I formmated both Swap and Ext4 partitions... the icons stayed there, but anyhow, it was an action that I hadn't done in the previous time.
I don't know exactly what was the action that solved the problem, since I have applied both... but one of them (or both combined) made it work.
Many thanks again for the post!
******* And WD Engineers:
For next models of My Could, please include a clean image in a safe partition (or even in an independed internal memory) and a button for a REAL factory reset, in order to make a full restauration and avoid all this problems to your customers.