Yes std c++ visual micro can't affect it unless it adds the project folder as compiler -I include path, that would give project  root <bar.h> and relative paths below project root <foo/bar.h>.

However a header in a folder with a .cpp where both are in a project sub folder might still be an issue, <bar.h> still wouldn't work in that case you would need <foo/bar.h> even if bar.cpp was in same folder as bar.h.

So it's clearer as it stands but more stringent. I think it's going to become an option

does it work if you uncheck vmicro>compiler>deep search?

Header files includes are case sensitive so make sure the case is correct.

This is a syntax or location error.

Please give a simple overview of where your files exist in windows explorer.

Thanks

In the arduino world there are .ino files. These files are combined into a standard cpp source during compile. For this to happen the build takes place in a temp build folder. 

Therefore the arduino world starts where your EmperorToolkitMega2560.ino and EmperorToolkitMega2560.vcxproj files are found.

You should consider folder outside of this directory structure to be excluded and non-valid.

The only way to have shared sources with normal arduino is to use a library which must be located in known locations.

Visual studio and visual micro do provide the ability to use shared sources from outside of the project tree but only under one of two clear sets of conditions. 

1) 

You would create a visual studio c++ shared project. Then add .cpp/h sources to it and use the References node below your arduino project to add a reference to the shared project. 

In this case visual micro will merge the sources (during compile) with the temp folder structure of the arduino project. Therefore a file in "SharedProject/Folder1/Header1.h" will be access from your .ino code as #include "Folder1/Header1"

or

2)  

You can create shared arduino library projects in a similar way using c++ shared projects. These projects must contain sources that follow the arduino library specification namely a library.properties text file in the root or each lib project.

Use the "create a project" on the visual micro "add library" menu to demonstrate how to create a library project. The option will create a project when you select a library to use in your code. You still need to use the "add reference" facility mentioned above so that intellisense and libs outside of std arduino locations can be discovered.

...

There is a final quick and dirty way. Add each of your shared sources to the as "links/shortcuts" using the vs "add existing item" menus. In this case visual micro will, during compile, copy sources to the root of the temp project folder. This means that regardless of where the sources are located your arduino code will reference them as if they are in the root of your arduino project.

...

There are some changes due out for the compiler which might help in the future but right now these are the best solutions.

Gosh, at last, someone who understands me