A lot of people (especially vincent) will say that I am talking out of my rear end here but ensure that you have a dir in C: named tmp (i had the same problem and this solved it).
And before I get any smug sarcastic relpies from people (vincent) I don't mean to put your include files in this dir, just have it present so that php knows its there.
Then call the include file using relative paths.
Hope this helps.
Let me know if this solves it please.
Cheers
Leon