Help:VE28
From TrainzOnline
The tag 'image' in containername must have an image file extension.
Where a container in a config.txt file includes the 'image' tag, the tag value must refer to a file name with an extension that indicates it is an image file.
For example, the first subcontainer in a thumbnails container was
0 { image "$screenshot$" width 240 height 180 }
which created the error:
- VE28: The tag 'image' in '0' must have an image file extension.
In this case the required fix was to change "$screenshot$" to "$screenshot$.jpg".
Valid image filename extensions include "jpg", "bmp", "tga" and "texture.txt".