老问题，但最近我也遇到了同样的问题.

Old question, but I had the same problem just recently.

您的 Assembly-CSharp.csproj 或 project-name.sln 文件中肯定存在问题.最可能是 .csproj 文件.如果您看一下它，将会看到对.dll文件的各种引用.

There must have been an issue in your Assembly-CSharp.csproj or project-name.sln files. Most likely to be the .csproj file. If you take a look at it, you will see various references to .dll files.

您可以通过启用编辑">首选项">生成所有.csproj文件"，告诉Unity(我的版本: v2019.2.20f1 )为您创建这些文件.

You can tell Unity (my version: v2019.2.20f1) to create these for you by enabling Edit > Preferences > Generate all .csproj files.

 1. Delete both files.
 2. Enable .csproj file generation.
 3. Double click on a script in Unity.

这解决了我的问题.