Undefined property

Thank for dave friend.
i use this code.

PHP Code:

$rows = $this->Product->get_product()->result(); 


The program runs through some time, but this problem is offline.

A PHP Error was encountered
Severity: Warning
Message: A non-numeric value encountered
Filename: controllers/ProductsUI.php
Line Number: 32
Backtrace:
File: C:\xampp\htdocs\accounting\application\controllers\ProductsUI.php
Line: 32
Function: _error_handler

PHP Code:

<td>'.$row->Cost.'</td>