I’m trying to follow the Space Shooter tutorial and get the same error “CS0103” …
I am under Windows 8.1 too.
Could this be related to a version of the .Net framework installed (or missing) on the system ?
Maybe trying to install a 3.5 version of the .Net framework for Windows 8.1 could do it, is it possible ?
Updated, some hours later :
In fact, it was : under Windows 8.1, only the 4.5 or 4.0 versions ('don’t remember) of the .net framework are installed and activated. The 3.5 is available, but not activated by default. After following the procedure given here : Installez .NET Framework 3.5 sur Windows 11, 10, 8.1, 8 - .NET Framework | Microsoft Learn, i have activated the 3.5 version (and after some additional file download), re-opened Unity 3D, checked my script (the GameController in the Space shooter tutorial) and IEnumerator is now properly identified and the script works !