It's very strange. In the Tamriel worldspace there is the file Mountainslab02.dds, so somewhere it exists. I have tried everything to find this file, so I can to add it to a worldspace, but with no luck. I go to Data, textures, but then I'm stopped in my tracks as there is no landscape folder..

Any ideas?

The file is packed in "Skyrim - Textures.bsa" and will need to be unpacked for you to use.

^this -- you will first need to unpack the bsa file - or alternatively create the folders and place a temp dds file in that position with the correct name and use it - then once you make the item using that texture go back and delete the temp file and the game will then use the one packed in the BSA.

EDIT : also looks like it's not Data/Textures/Landscape/Mountainslab.dds but Data/Textures/Landscape/Mountains\Mountainslab01.dds or Data/Textures/Landscape/mountains/Mountainslab02.dds

Ah right. So I downloaded BSA Unpacker and it gives these instructions:

By the way I was just watching a tutorial 'Creation Kit Tutorials - Worldspace LOD' and it happened to be by you, coincidence

....and Falskaar. I have it added to my Skyrim, have done for a while now, fantastic mod and when Nexus sorts the bug on my account I will be sure to endorse it!

Thanks for this advice, I'll give that a go if I can't figure out the BSA Unpacker!

The BSAs are actually in the DATA folder not the Skyrim folder !

Lol ok... hmmm i guess the instructions are wrong.

Thanks and btw I went with BSA Browser, it unpacked all the textures in the game for me without any issues.