Ecshop Vietnam Application Error

The application could not run because of the following error:

Type: E_NOTICE [8]

Message: Undefined variable: slug in /home/ixfdqnemhosting/public_html/bachkhoacuocsong.com/modules/article_cat.php

Line: 16

Stack trace:

#0 /home/ixfdqnemhosting/public_html/bachkhoacuocsong.com/modules/article_cat.php(16): ErrorHandler->handleError(8, 'Undefined varia...', '/home/ixfdqnemh...', 16, Array)
#1 /home/ixfdqnemhosting/public_html/bachkhoacuocsong.com/index.php(24): include_once('/home/ixfdqnemh...')
#2 {main}