My first guess would be that the project configuration is broken. Does this error still persist if you delete the Intermediate, DerivedDataCache and Saved folders and re-generate your project files?
Can you tell us what should be in the paths instead of ??? (probably M2 or ykyu)? Do you have a clue what change on your project (or the engine or your system) might have introduced this error?
I don’t think that the drive should matter too much, but for now I really would recommend a conservative handling of your paths and trying to avoid any non-ANSI and whitespace characters in them. Then it would be good if you could provide a build log as it possibly could contain further hints on what is going wrong.
Your first problem is that you might be using extended UTF-8 characters that are not ASCII; UE4 does not currently support UTF-8 in path-naming systems. That is, rename your folders and files that are part of the project’s path such that there will be no UTF-8 extended characters(just use ASCII). Your second problem is that in order to build your project, your currently installed MVS C++ compiler toolchain requires you to have a version of the SDK in order to build the project on your machine. So you might want to google that.