correct folder is:
[UserData]\Work\Items\Stadium(or Common, Canyon etc.)\YourObjectNameFolder
YourObjectNameFolder must be this way:
YourObjectNameFolder\
YourObjectNameFolder\Icon
YourObjectNameFolder\Meshes
YourObjectNameFolder\Meshes\Texture
so we got 4 folders in total for one object inside the work folder, it looks like this now:

I used here as example the Common folder collection but this can also be Stadium, Valley etc.
Toplevel
YourObjectName folder contains the
YourObjectName.Item.xml file
Folder
Icon contains your icon (24bit tga file)
Meshes folder contains your
YourObjectName.fbx
Texture folder contains your object textures (f.e. YourObjectName_D.tga, YourObjectName_N.tga, YourObjectName_S.tga)
all tga files have to be 24bit tga (these ones with alpha channel have to be 32bit tga), the nadeo importer convert these tga files to the right dds format (but you can also add only dds files in the texture folder but these have to be the right dds format)
make sure you set the right environment inside the convert assistant which matches to your folder structure and all works
this works 100%
All objects will be imported into the "newly" folder structure:
[UserData]\Items\Stadium(or Common, Canyon etc.)\YourObjectNameFolder
[UserData] is the folder you set on the install as your personal data folder, can be found by clicking in the start launcher on help (and there you can move your personal data to a different location on your hdd)