I just recently went through this exercise for the first time, so it's fresh on the brain. I started a route using a built-in template, and changed to my own template later on. Perhaps this will help:
Does your route have its own route template, or are you using one of the built-in route templates?
Route templates for your route are in the Assets folder under Provider\Product (these are names you provide). This forms the root of your assets for your route. Here there would be a folder named "templateRoutes". Here is where your route template is stored. Within the blueprint file for your route is the pointer to the loading picture. The dds itself should also be in the folder, with the extension TgPcDx. This would have been created from your DDS by RW_Tools.
Your RouteProperties file also needs to know where your route template file is located. This is the file called RouteProperties.xml, and is located in your Routes folder. You can edit this file with RW_Tools. The entry is blueprintid, and here you tell it your provider, product, and name of your route template file.
What was happening to me was RW_Tools was placing the final TgPcDx in the built-in assets folder instead of mine (in my case, Kuju\RailSimulatorUS).
Getting all the pointers pointing, and the final graphic placed in its correct folder solved it for me.
Pax,
P.
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