problem with a .asset

Unity Engine
1

Hello everyone,
I have a file.asset looking like a shader, and it contains a lot of other files like animations, materials…

I would like to extract them. I have found some softwares (unity asset explorer / asset bundle extractor…), but none of them works : the reason seems to be the extension of the file which is .asset instead of .assets ?
It driving me crazy, as everytime I open my project I have that error :

ApplicationException: Unable to find a suitable compiler for sources with extension ‘asset’ (Output assembly: Temp/Assembly-UnityScript.dll)
UnityEditor.Scripting.ScriptCompilers.CreateCompilerInstance (MonoIsland island, Boolean buildingForEditor, BuildTarget targetPlatform, Boolean runUpdater) (at C:/buildslave/unity/build/Editor/Mono/Scripting/ScriptCompilers.cs:96)
Failed to create compiler instance

If you have any tip, I would be really gratefull.

2

Where did it come from?

3

Hello zombiegorilla,
I had downloaded it on the assetstore a long time ago, but now I can’t find it anymore, neither a new version of it. I guess I will use different assets if this one continue not to work.