You probably just need to have import statements for these classes in your code:
It looks like whoever wrote that tutorial forgot to add those. If you were typing in the code rather than pasting it in, the import statements would get automatically added, so maybe the author just didn't notice that they were necessary.
Related Flex Builder tip:
If you get this error for any class, it means that the compiler can't find the class definition (which usually means you're missing an import statement). The easiest way to add the import statement is to put your cursor at the end of the class name (e.g. right after the word File) and hit Ctrl-Enter (on Windows -- probably Cmd-Enter on Mac). Ctrl-Enter is the shortcut to trigger a code hint, but if you trigger it that way it will recognize the class and just add the import statement for you.
I imorted flash.filesystem.* and it still doesn't work.
Thanks for the import tip however, I needed to know that!
This should be simple. You probably somehow misplace your code.
If you could post your code here, people should be able to help you.