I had the same problem after installing PhotoPost and choosing
VB enhanced integration over the weekend.
Omegatron found my problem. Check the path in you index.php file in your forum directory.
The path to my files was wrong. The information in the post documentation is an example, not an absolute. In the index.php ./ is for a directory in your forums directory. Since my photopost folder was not there and it was back one level..
instead of...
include('./photopost/inc_features.php');
include('./photopost/inc_photopost.php');
mine needed to be...
include('../photopost/inc_features.php');
include('../photopost/inc_photopost.php');