Open the project file and remove all references with Import Project="..\packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.1.0.0....
Open web.config and remove all system.codedom compilers attributes
Open the project file and remove all references with Import Project="..\packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.1.0.0....
Open web.config and remove all system.codedom compilers attributes