You can open the .tscn file that is failing to load with notepad or some other text editor and make sure that all paths inside are correct.
A scene file looks something like this:
[gd_scene load_steps=11 format=2]
[ext_resource path="res://textures/dice.png" type="Texture" id=1]
[ext_resource path="res://scripts/ui/Dice.gd" type="Script" id=2]
[sub_resource type="AtlasTexture" id=1]
atlas = ExtResource( 1 )
region = Rect2( 1, 0, 64, 64 )
Notice how you have
path="res://... lines. You need to update those to point to valid files in your project. Also, note that the path is case-sensitive, i.e. small and capital letters matter.