I've got an update on this problem. My webhost was able to track down the problem, which appears to be a bug in the latest version of PHP which has been documented at:
http://bugs.php.net/bug.php?id=24053
The include for PluhNews is actually working, however the error message is displayed. A quick fix is to place an @ symbol in front of the include to suppress the error message.
The bottom line is that it's a bug in PHP which will most likely be addressed in a future update, however there appears to be several temporary work arounds for this issue