db_insert_error on wp_insert_post

I’m making a modified version of a plugin called Event RSVP.
The original plugin works fine, but my version returns the following error:

WP_Error Object
(
    [errors] => Array
        (
            [db_insert_error] => Array
                (
                    [0] => Could not insert post into the database
                )

        )

    [error_data] => Array
        (
        )

)

The code I’m using is:

$post = array(
	    'post_title'     => 'skidaskoli-registration-' . sha1( $name ), //Create unique title. is it necessary ?
	    'post_status'    => 'publish',
	    'post_type'      => 'skidaskoli-registration',
	    'post_parent'    => $event_id,
	    'post_date'      => date( 'Y-m-d H:i:s', time() )
	);
	$post_id = wp_insert_post( $post, true );

code from original plugin is:

$post = array(
	    'post_title'     => 'ersvp-registration-' . sha1( $name ), //Create unique title. is it necessary ?
	    'post_status'    => 'publish',
	    'post_type'      => 'ersvp-registration',
	    'post_parent'    => $event_id,
	    'post_date'      => date( 'Y-m-d H:i:s', time() )
	);
	$post_id = wp_insert_post( $post );