Could you go into Project Properties->Build->Variables tab, enable the "Show system variables" check box and verify that PROJECT_ROOT is set to the correct path where your project is located.
If so, please capture screenshots of the following, place them in a zip file and attach it here, so we can take a look at it:
1) your C source file in the editor view that shows the "?" sign
2) Your compiler include path settings dialog (under Project Properties->Build->Compiler->Include Options
3) build output in the CCS build console - it might be easier to copy and paste the full output to a text file