Problem with theme

[sandy]

Here is development URL

http://seorants.com/projects/naturemart/

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3bcfdf56-3da3-457e-9ddf-b38ed5ed8942 – 11 Apr 2015 (Regular License)
Here is issue: slider is not working and sidebar as well
Here is error I am getting
CATEGORY
Fatal error: Call to undefined method Mage_Catalog_Helper_Category_Flat::isAvailable() in /home/seorants/public_html/projects/naturemart/app/code/local/Sns/Ostore/Block/Navigation.php on line 28

Please help me to fix it.

Thanks,
Sandy

[Author]

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