Problem with hidden chars

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Hi,

I’m using a template who strip the content to create excerpt, the problem is that once in a while (but getting more frequent now) it happens to find a hidden chars (not identified yet) which will prevent it from stripping the content and would give away an error like this:

Warning: Wrong parameter count for substr() in /../wp-content/themes/tk/functions.php on line 160

Which is:

$content = substr($content, 0, $espacio, "utf-8");

The whole function is:
function wp_limit_post($max_char, $more_link_text = '[...]',$notagp = false, $stripteaser = 0, $more_file = '') {
		$content = get_the_content($more_link_text, $stripteaser, $more_file);
		$content = apply_filters('the_content', $content);
		$content = str_replace(']]>', ']]>', $content);
		$content = strip_tags($content);

	   if (strlen($_GET['p']) > 0) {
	   	  if($notagp) {
		  echo mb_substr($content,0,$max_char, "utf-8");
		  }
		  else {
		  echo '<p>';
		  echo mb_substr($content,0,$max_char, "utf-8");
		  echo "…</p>";
		  }
	   }
	   else if ((strlen($content)>$max_char) && ($espacio = strpos($content, " ", $max_char ))) {
			$content = substr($content, 0, $espacio, "utf-8");
			$content = $content;
			if($notagp) {
		    echo mb_substr($content,0,$max_char, "utf-8");
			echo $more_link_text;
		    }
		    else {
			echo '<p>';
			echo mb_substr($content,0,$max_char, "utf-8");
			echo $more_link_text;
			echo "…</p>";
			}
	   }
	   else {
	      if($notagp) {
		  echo mb_substr($content,0,$max_char, "utf-8");
		  }
		  else {
		  echo '<p>';
		  echo mb_substr($content,0,$max_char, "utf-8");
		  echo "…</p>";
		  }
	   }
	}

To repair this manually I have to delete one phrase after the another know where is the hidden chars, then when I find the phrase I have to delete it and rewrite it directly into WordPress, and it will work. This is quite a pain as this is happening almost once a week now.

Thanks for your help,
Rui