The function.php of this theme contains these lines of code (1880-1884):
function show_post( $ID ) {
$post = get_page( $ID, 'edit' );
$content = apply_filters('the_content', $post->post_content);
echo $content;
}
Add Global $post; in the line below function show_post(. It should look like this:
function show_post( $ID ) {
Global $post;
$post = get_page( $ID, 'edit' );
$content = apply_filters('the_content', $post->post_content);
echo $content;
}
You can use the editor in Site Admin > Appearnce > Themes > Editor. Or you download the functions.php file via FTP from your blog to your local computer and use a text editor (not MS Word or other Office software) to edit the file. Afterwards upload the file again. (You can also use the second way if something goes wrong while editing the functions.php file with the WP-own editor.)
This should resolve the problem.