[...]
Try the following:
1) include() will only trigger a warning if the requested file is not within the include path. Thus, to make sure the file is found, you should use "require()" which triggers a fatal error and prevends the script from being executed if the given filename as the parameter cannot be found. This will give you probably a hint if there's something wrong with the include-path
2) Another suggestion would be to prepend "./" to the file you try to include:
instead of
include("file.php");
you should use
include("./file.php");
"./" indicates that php should lookup the requested file in the directory the php-file resists in which called the include()-function.