What?
If you get something like the following error:

Warning: call_user_func() [function.call-user-func]: First argument is expected to be a valid callback in /home/.../templates/rt_affinity/rt_sectionrows.php on line 311

How?

  1. Copy & backup the file /public_html/.../templates/rt_affinity/rt_sectionrows.php
  2. Find the following piece of code around line 311: 
    foreach($this->horizontalCookie[$row] as $block) {
	$block = str_replace('-', '', $block);
	$this->module_row1 .= call_user_func($block, $this, $mClasses);
}
  3. And change it to: 
    foreach($this->horizontalCookie[$row] as $block) {
	if(!empty($block)) {
		$block = str_replace('-', '', $block);
		$this->module_row1 .= call_user_func($block, $this, $mClasses);
	}
}