Fatal error: Call to a member function toOptionArray() on a non-object

I have installed a new module then suddenly I got a fatal error in admin like Call to a member function toOptionArray() on a non-object in app/code/core/Mage/Adminhtml/Block/System/Config/Form.php on line 46.

To solve this issue go to app\code\core\Mage\Adminhtml\Block\System\Config\Form.php

Now find the following on line 463

$optionArray = $sourceModel->toOptionArray($fieldType == 'multiselect');

replace this with below code:

if(is_object($sourceModel)){
	$optionArray = $sourceModel->toOptionArray($fieldType == 'multiselect');
} else {
	Mage::log($e->source_model);
}

Hope this tutorial will help you to solve the Fatal error: Call to a member function toOptionArray() on a non-object issue.