When adding existing files or folders to a project, consider the name restrictions discussed in Path, File and Folder Name Restrictions. Specifically, take care with long paths. Although there is a known limit for Windows OS (path length of 260 characters, command line of 8191 characters), a very long path on other systems may cause issues. If you have problems building, consider shortening long paths or moving files or folders into the project folder.
To ensure the most portable project, use relative paths when importing files or folders.