sorry, but like Spooks I can see no reason why that code would not work under any circumstances unless there was a problem with the include path in the php.ini, in saying that I see you tried the absolute path which should work in anycase.
I used include './sample_array.txt';
but all of your methods should have worked with the possible exception of $DOCUMENT_ROOT which may give a misleading value in a script aliased directory (and is best now accessed via $_SERVER[DOCUMENT_ROOT]
try running this to see if your include path has anything strange in it
MVC is the current buzz in web application architectures. It comes from event-driven desktop application design and doesn't fit into web application design very well. But luckily nobody really knows what MVC means, so we can call our presentation layer separation mechanism MVC and move on. (Rasmus Lerdorf)