Error processing checkout. Please try again.

i have add wooquickpay plugin but i have checkout the order it is give me a error like “Error processing checkout. Please try again.” i dont why. i check in firebug

error:
Fixed malformed JSON. Original:
<b>Notice</b>: Trying to get property of non-object in <b>/var/www/html/kamagra/wp-content/plugins/woocommerce-quickpay/woocommerce-quickpay.php</b> on line <b>496</b><br />
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<b>Notice</b>: Trying to get property of non-object in <b>/var/www/html/kamagra/wp-content/plugins/woocommerce-quickpay/woocommerce-quickpay.php</b> on line <b>501</b><br />
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<b>Notice</b>: Trying to get property of non-object in <b>/var/www/html/kamagra/wp-content/plugins/woocommerce-quickpay/woocommerce-quickpay.php</b> on line <b>502</b><br />
<br />
<b>Notice</b>: Trying to get property of non-object in <b>/var/www/html/kamagra/wp-content/plugins/woocommerce-quickpay/woocommerce-quickpay.php</b> on line <b>508</b><br />
{“result”:”failure”,”messages”:””,”refresh”:”false”,”reload”:”false”}