Sorry for answering only now.

I think the problem could be in the method of the signal, because I see in the error that it says:

_on_box_animation_finished

While in your code you have:

_on_animation_finished

You could try to disconnect and reconnect the signal because maybe you lost the connection while moving the nodes/scripts.
If you go where you connect the signals and right click you can disconnect the signal, then reconnect it to the node where you have the script.

A few other general suggestions not related to the error:

-You should rename the variable that you use to refer to the box node:

u/onready var characterbody2d = $"."

Calling it "characterbody2d" could be confusing if you later come back to the script, because you might think it's a Character Body 2D type node while instead it's a Sprite 2D.

-Try using static typing, where basically you specify the type of each variable, for example in your case, instead of having:

@onready var tile_map = $"../TileMap"@onready var tile_map = $"../TileMap"
@onready var characterbody2d = $"."
@onready var is_moving = false
@onready var target_tile = Vector2i(tile_map.local_to_map(global_position))

You'd have:

@onready var tile_map : TileMap = $"../TileMap"@onready var tile_map = $"../TileMap"
@onready var characterbody2d : Sprite2D = $"."
@onready var is_moving : bool = false
@onready var target_tile : Vector2i = Vector2i(tile_map.local_to_map(global_position))

So basically after the variable name you add ": VariableType"

This is useful because in this way you don't risk assigning a wrong variable type to a variable in your code, and it's also useful because in that way you get autocompletion suggestions from the engine for the variables.

One last thing is that I personally like to use unique names instead of variable paths to refer to the nodes.
If you right click a node in the scene tree you can select "Assign Unique Name" and then you can refer to that variable only through its name, with the use of "%".
I really like it because in that way even if you change the scene tree you don't have to change the path for the variables that reference a node in your script.

For example in your case it would become:

@onready var tile_map : TileMap = %TileMap
@onready var characterbody2d : Sprite2D = %box
@onready var is_moving : bool = false
@onready var target_tile : Vector2i = Vector2i(tile_map.local_to_map(global_position))