FS_file functions are from a GameMaker:Studio extension that not a lot of fangames use anymore. Klazen's engine just so happens to use it, and it appears that you're missing the extension, which is making gamemaker spit out those errors telling you it doesn't know what those FS_file functions mean.
When you followed Klazen's guide, you should've downloaded his project file. If you go to the extensions folder in the GMS_Engine_KS_Edition.gmx folder the file should be there. The file you're looking for is GMFileSystem.extension.gmx You can drag-and-drop that file into your project to add it, that should fix your problem.
Good luck making games!