Firstpass.dll is a binary file and not a text file.

Unity Engine
1 
Internal compiler error. See the console log for more information. output was:error CS2015: Source file `Assets/Plugins/Editor/AdvancedInspector/Assembly-CSharp-firstpass.dll' is a binary file and not a text file

For some reason, I had to move some of my code into the Plugins folder, mainly so that multiple language (C#, Javascript) can access it.

However, any time a change is done to any script, Unity recreates a .DLL named Assembly-CSharp-firstpass.dll in the Plugins folder and output that error.

If I delete the .DLL, everything works and compiles just fine… Until I edit any script. That stuff is for the AssetStore, so telling people to just delete a .DLL that keeps coming back is a no-go. Shouldn’t that DLL be compiled in Library/ScriptAssemblies?

2

For some reason, after having trash the .SLN, Library and almost everything else in the project, the error is gone. Still no idea why Unity kept copying that .DLL over in the project.