Visual Studio compiles fine, but it still shows red lines
Visual Studio 2017:
Closing Visual Studio and removing the .vs folder located in the solution directory worked for me.
This folder has a hidden attribute. You may need to change settings in folder options to show hidden files.
Delete the contents of the temporary ASP.NET folder and then rebuild. It'll either be in your user folder (for IIS Express - \AppData\Local\Temp\Temporary ASP.NET Files) or the Windows directory (for IIS - C:\Windows\Microsoft.Net\Framework\vx.xx\Temporary ASP.NET Files)
Paths are off the top of my head and may not be correct