Hi.
Yeah, that's my bad actually.
srpl_empty.dds s located in SkyFiles folder - copy it from there and everything should work.
As for re-opening exported files in other tools it's not gonna work. These shaders go a little beyond what GMT files were meant for, so I'm using things like texture UV coordinates to store parameters like flare radius for example. Standard editors meant for rFactor won't be able to handle files exported from my tool. Whatever you export - it's final.
Of course you can still work on your meshes, by editing original GMT files (these without shaders) and when you load your project in my tool again - you will see all your changes. The only thing you need to do is re-export.
That's why this tool does not modify any GMT file you added to your project - they remain untouched on disk, so you can still work on them. New GMT files with shaders are exported to another folder.
EDIT:
I quickly prepared this image to show the idea:
On the left is some standard workflow - you work on .GMT files using some editor and then you put that file into rFactor.
On the right is workflow with my material tool - you work on .GMT files the same way, using 3D Studio and then let my tool add shaders on top of that, based on information in the project file.
What's marked in green are files you actually work on using these tools.