Slideshow doesn't work

You have strange content on the page:

<script type='text/javascript' src='http://wppa.opajaap.nl/wp-content/plugins/wp-photo-album-plus/wppa.min.js?ver=3.6-alpha-23451'></script>

It should be:

<script type='text/javascript' src='http://www.opentennisgravenchon.org/wp-content/plugins/wp-photo-album-plus/wppa.min.js?ver=5-1-16-000'></script>

And appear earlier on the page.

Is there any form of speedup or minifying setting in your theme?
An old version of wppa.js ( or wppa.min.js ) is used that is not compatible with the current version.

This:

<script type='text/javascript' src='http://www.opentennisgravenchon.org/wp-includes/js/jquery/jquery.js'></script>
<script type='text/javascript' src='http://www.opentennisgravenchon.org/wp-includes/js/jquery/jquery-migrate.js'></script>
<script type='text/javascript' src='http://www.opentennisgravenchon.org/wp-content/plugins/wp-photo-album-plus/wppa.min.js?ver=5-1-16-000'></script>

must come BEFORE:

<!-- WPPA+ Runtime parameters -->
	<script type="text/javascript">
	/* <![CDATA[ */

	wppaDebug = false;
	wppaVersion = "5-1-17-003";
...etc

because you are overwriting the runtime parameters with the defaults from the js file.

Why did you modify your theme’s header.php ?
Do you know what you are doing?
Why is the wppa.min.js file not loaded normally?