Critical Error after Including php File into Plugin Main File

Hello everybody,

i am new in plugin development and i cant find the solution for the following problem:

I am working on a plugin for buddypress. After including a php file via include() into the main plugin file i am getting the status critical error at the frontend.

The php file contains html and php functions. The content inside the php file should be displayd after a certain element is clicked.

The code of the main plugin file looks like this:

<?php
/*
Plugin Name: CGTpushGroup

*/

include_once(plugin_dir_path( __FILE__ ) . 'CGTgroups.php' );

add_action( 'wp_enqueue_scripts', 'my_plugin_assets' );

function my_plugin_assets() {
    wp_enqueue_style( 'CGTstyle', plugins_url( '/public/CGTOverlaygroups.css' , __FILE__ ), null, null, true);
    wp_enqueue_script( 'postGroup', plugins_url( '/public/CGTpostGroupActivityStream.js' , __FILE__ ), null, null, true);
    wp_enqueue_script( 'sessionStorage', plugins_url( '/public/CGTsessionStorageRecipe.js' , __FILE__ ), null, null, true);
    wp_enqueue_script( 'clickOverlay', plugins_url( '/public/CGTclickOverlay.js' , __FILE__ ), null, null, true);
}

?>

And the code / markup in the including php file looks like this:

<?php
<div id="CGToverlay">
    <div id="text">
        <?php if ( bp_has_groups('user_id=true') ) : ?>
            <ul id="groups-list" class="item-list">
                <?php while ( bp_groups() ) : bp_the_group(); ?>

                    <li>
                        <div class="item-avatar">
                            <a href="<?php bp_group_permalink() ?>"><?php bp_group_avatar( 'type=thumb&width=50&height=50' ) ?></a>
                        </div>

                        <div class="item recipeclick" style="border:1px solid #CCC; background: green;">
                            <div class="item-title"><a href="<?php bp_group_permalink() ?>"><?php bp_group_name() ?></a></div>

                            <div class="item-desc"><?php bp_group_description_excerpt() ?></div>

                            <?php do_action( 'bp_directory_groups_item' ) ?>
                        </div>

                        <div class="clear"></div>
                    </li>

                <?php endwhile; ?>
            </ul>

            <?php do_action( 'bp_after_groups_loop' ) ?>

        <?php else: ?>

            <div id="message" class="info">
                <p><?php _e( 'There were no groups found.', 'buddypress' ) ?></p>
            </div>

        <?php endif; ?>
    </div>
</div>
?>

I will be very grateful if anybody could help me.

Best regards
Thomas