Warning call_user_func: First argument is expected to be a valid callback

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:
   copyrawstyler

   foreach($this->horizontalCookie[$row] as $block) {
   	$block = str_replace('-', '', $block);
   	$this->module_row1 .= call_user_func($block, $this, $mClasses);
   }

   1.  foreach($this->horizontalCookie[$row] as $block) { 
   2.      $block = str_replace('-', '', $block); 
   3.      $this->module_row1 .= call_user_func($block, $this, $mClasses); 
   4.  } 
3. And change it to:
   copyrawstyler

   foreach($this->horizontalCookie[$row] as $block) {
   	if(!empty($block)) {
   		$block = str_replace('-', '', $block);
   		$this->module_row1 .= call_user_func($block, $this, $mClasses);
   	}
   }

   1.  foreach($this->horizontalCookie[$row] as $block) { 
   2.      if(!empty($block)) { 
   3.          $block = str_replace('-', '', $block); 
   4.          $this->module_row1 .= call_user_func($block, $this, $mClasses); 
   5.      } 
   6.  }