Help me get the excerpt!

Hi there.. I try to modify a widget to show what i want… But i can’t get the excerpt to show! Can you help me with this ?

function widget( $args, $instance ) {
		extract( $args );

		/* Our variables from the widget settings. */
		$title = apply_filters('Recent Posts', $instance['title'] );
		$post_cat = $instance['post_cat'];
		if($post_cat == "All"){ $post_cat = ''; }
		$show_num = $instance['show_num'];

		/* Before widget (defined by themes). */
		echo $before_widget;
		if($title)
			echo $before_title . $title . $after_title;

		/* Display the widget title if one was input (before and after defined by themes). */
		$custom_posts = get_posts('showposts='.$show_num.'&cat='.get_cat_ID($post_cat));
		if( !empty($custom_posts) ){
			echo "<div class='gdl-recent-conference-widget'>";
			foreach($custom_posts as $custom_post) {
				?>
				<div class="recent-conference-widget">
					<div class="recent-conference-widget-thumbnail">
						<a href="<?php echo get_permalink( $custom_post->ID ); ?>">
							<?php
								$thumbnail_id = get_post_thumbnail_id( $custom_post->ID );
								$thumbnail = wp_get_attachment_image_src( $thumbnail_id , '280x111' );
								$alt_text = get_post_meta($thumbnail_id , '_wp_attachment_image_alt', true);
								if( !empty($thumbnail) ){
									echo '<img src="' . $thumbnail[0] . '" alt="'. $alt_text .'"/>';
								}
							?>
						</a>
					</div>
					<div class="recent-conference-widget-context">

						<p>
							<?php echo get_the_excerpt( $custom_post->ID ); ?>
						</p>

						<a href="<?php echo get_permalink( $custom_post->ID ); ?>">
							Read More
						</a>
					</div>
					<div class="clear"></div>
				</div>
				<?php 

			}
			echo "</div>";
		}
		/* After widget (defined by themes). */
		echo $after_widget;
	}

Thx in advance