Imagetable is nil

Simulator version: 2.6.2
API version: 20601

Am I referencing this PNG file correctly?

The error is:

Load failed, error: Tilemap/TileMap.lua:5: file walls not found: No such file
stack traceback:
	[C]: in function 'assert'
	Tilemap/TileMap.lua:5: in main chunk
stack traceback:
	[C]: in function 'import'
	main.lua:7: in main chunk
Update error: Tilemap/TileMap.lua:5: file walls not found: No such file
stack traceback:
	[C]: in function 'assert'
	Tilemap/TileMap.lua:5: in main chunk
stack traceback:
	[C]: in function 'import'
	main.lua:7: in main chunk

It looks like it's looking for a file called walls rather than walls-table-32-32.png.
![walls-table-32-32|96x96, 50%]

Here's the actual walls-table-32-32.png

walls-table-32-32

The path needs to be relative to the root, not relative to the file.

e.g. I need "Tilemap/walls".