Further to the advice above, everything the asset needs to work must be in the assets folder or directly accessible in the folders of other assets.
This applies to the:-
- config.txt file
- the thumbnail file - it does not have to be called thumbnail.jpg but it must be a .jpg image and its name must be in the config.txt file
- the mesh file - if it is a visible object (house, tree, fence, blade of grass, etc)
- any sound files - have to be .wav file format
- any images (.jpg, .tga, .png are the most commonly used) and .html files for HTML assets
- any script files - if applicable
must all be inside the asset.
If this is your first asset then I suggest you look at the Trainz Wiki for instructions. For example:-
https://online.ts2009.com/mediaWiki...e_a_HTML_Asset#How_to_Create_a_New_HTML_Asset for creating a HTML asset
https://online.ts2009.com/mediaWiki...e_a_Region_Asset#How_to_Create_a_Region_Asset for creating a region asset
https://online.ts2009.com/mediaWiki..._Create_a_New_Non-Environmental_Texture_Asset for creating a non-environmental texture asset.
Each type (KIND) of asset has its own rules as to what has to be included and what is optional. Likewise, the contents of the config.txt file is different for each type of asset.