A few of the users have been complaining about this issue in Connections theme and I believe it will be the same case in other themes too.

Fatal error: main(): Failed opening required ‘post.php’
To resolve this problem, please open up the index.php file and look for the line

< ?php require(‘post.php’); ?>

and change it to

< ?php require(TEMPLATEPATH . ‘/post.php’); ?>

Hope that solves the problem.

– Sadish