minimalnet

Finally seems was k2 template problem, i removed this lines in the configuration and now seems work fine:

// Get the asides category
	$asides_id = get_option('k2asidescategory');
	$asides_title = $asides_id != 0 ? $wpdb->get_var("SELECT cat_name from $wpdb->categories WHERE cat_ID = $asides_id LIMIT 1") : __('No Asides','k2_domain');

	// Get the categories we might use for asides
	$asides_cats = $wpdb->get_results("SELECT cat_ID, cat_name FROM $wpdb->categories");

			<h3><?php _e('Asides','k2_domain'); ?></h3>

			<p><small><?php _e('\'Asides\' is a category of entries, meant to be \'smaller\' and perhaps of \'less importance\', like for instance links with minor commentary. They are styles differently than other entries to separate them content-wise. Below you can select a category to be shown as Asides.','k2_domain'); ?></small></p>

			<p>
				<select id="k2-asidescategory" name="k2[asidescategory]">
					<option value="0" <?php selected($asides_id, '0'); ?>><?php _e('No Asides','k2_domain'); ?></option>

					<?php foreach ($asides_cats as $cat) { ?>
					<option value="<?php echo attribute_escape($cat->cat_ID); ?>" <?php selected($asides_id, $cat->cat_ID); ?>><?php echo($cat->cat_name); ?></option>
					<?php } ?>
				</select>
			</p>

I have tried to do a test, to install the version 2.13, update, all fine then, but after install the 2.3 version again the same error.