Custom column-event date,admin area- problems-publish button leads to blank scr

Hello, I have a custom post type called “hks-najave” (“najave” means “future events”), very basic and simple post type for storing events:
-title
-description
-event date ( I do not need start-end dates, just simple single date)
-featured image
(people can add category and tags – optionaly)

I am still learning about custom post types and here I did well with registering my cpt hks-najave and with querying, displaying and sorting events (begining from most recent )on my custom page template.
Even dates I managed to display the way/format I want.

But I have a problem with cpt list in admin area. By default, in my admin area for custom post type hks-najave I can see the basic few columns: title, category, tag, and date when the post was published.

I have a custom field “datum-najave” that stors event date.
So far I managed to make/add a new column and even make the column sortable, but the code I add to my functions.php causes me problems:
– when I want to add new custom post and publish it it leads me to blank screen.
Post is added but something is going wrong after clicking “publish” since I get the blank screen.
Same thing with normal, regular posts. Blank screen after hitting “publish” or “move to trash”.
And when I want to add featured image – images in media library are not showing.

When I remove the code from functions.php everything is ok again.

This is the code:

<?php

// Register a new column in the admin Post area

add_filter('manage_edit-hks-najave_columns', 'my_dat_najave_column');
function my_dat_najave_column($columns) {
    $columns['datumnajave'] =__('Datum najave');
    return $columns;
}  

// add content

add_action( 'manage_hks-najave_posts_custom_column', 'my_dat_najave_column_content', 10, 2 );
function my_dat_najave_column_content( $column_name, $post_id ) {
    if ( 'datumnajave' != $column_name )
        return;
    //Get dates from post meta
    $datumnajave = get_post_meta($post_id, 'datum_najave', true);
    echo intval($datumnajave);
}  

//  make the column sortable

add_filter( 'manage_edit-hks-najave_sortable_columns', 'my_sortable_datum_column' );
function my_sortable_datum_column( $columns ) {
    $columns['datumnajave'] = 'datum';  

    //To make a column 'un-sortable' remove it from the array
    //unset($columns['date']);  

    return $columns;
}  

add_action( 'pre_get_posts', 'my_datum_orderby' );
function my_datum_orderby( $query ) {
    if( ! is_admin() )
        return;  

    $orderby = $query->get( 'orderby');  

    if( 'datum' == $orderby ) {
        $query->set('meta_key','datum_najave');
        $query->set('orderby','meta_value_num');
    }
}  ?>

Maybe you can figure out why this code is causing me problems.
Column is displaying, and it is sortable – only dates are not in pretty format but i will work on that.

But I can not leve the code there since it causes problems during publishing.
Site is running with wp 3.5.2, in a next few days I will update it,
but I think the wordpress version is not the reason of the problem …

Maybe there is a better way to add custom column to cpt, with dates.
My cpt name is “hks-najave” , custom field with date is called: ” datum_najave “.
Thanks