Help!

I am facing a error

. The game doesn't starts, and at the loading screen it gives me error 'RGL ERROR: Unable to open file: Modules\1257ad\Resource\skyboxes.brf'
Any way to fix it? I am missing this mod very much
Will this work for Diplomacy mod?
When I try to open it, it gives me an error. A horrible error, which reopens again and again after you close it. So I had to end it's process.