Error on frontpage on activate events+ ( wizer theme )

When i activate the events+ plugin, appears an error on front page.

Fatal error: Call to a member function is_main_query() on a non-object in /home/storage/0/40/9e/muonlinebr1/public_html/danceadois/v3/portal/wp-includes/query.php on line 724

The block on my frontpage that causes the error

<div id="post-title"><span>Latest News</span></div>

<?php $temp = $wp_query; $wp_query= null; $wp_query = new WP_Query('showposts=15&cat=&paged=' . $paged);?>
<?php $postcounter = 0; if ($wp_query->have_posts()) : ?>
<?php while ($wp_query->have_posts()) : $postcounter = $postcounter + 1; $wp_query->the_post();?>

<div class="post-meta" id="post-<?php the_ID(); ?>">
<?php if ( has_post_thumbnail() ) { ?>
<div class="thumb"><?php the_post_thumbnail(array(100,100), array('class' => 'alignleft')); ?></div><!-- THUMB END -->
<?php } ?>

Please help .. this plugin is very important to me.

My site url http://dd.danceadois.com.br/v3/portal