The requested Payment Method is not available.

#0 /home/partmonster/public_html/app/code/core/Mage/Payment/Model/Info.php(82): Mage::throwException('The requested P...')
#1 /home/partmonster/public_html/app/code/core/Mage/Sales/Model/Quote/Payment.php(218): Mage_Payment_Model_Info->getMethodInstance()
#2 /home/partmonster/public_html/app/code/core/Mage/Authorizenet/Block/Directpost/Form.php(72): Mage_Sales_Model_Quote_Payment->getMethodInstance()
#3 /home/partmonster/public_html/app/code/core/Mage/Core/Model/Layout.php(348): Mage_Authorizenet_Block_Directpost_Form->setMethodInfo()
#4 /home/partmonster/public_html/app/code/core/Mage/Core/Model/Layout.php(214): Mage_Core_Model_Layout->_generateAction(Object(Mage_Core_Model_Layout_Element), Object(Mage_Core_Model_Layout_Element))
#5 /home/partmonster/public_html/app/code/core/Mage/Core/Model/Layout.php(206): Mage_Core_Model_Layout->generateBlocks(Object(Mage_Core_Model_Layout_Element))
#6 /home/partmonster/public_html/app/code/core/Mage/Core/Model/Layout.php(210): Mage_Core_Model_Layout->generateBlocks(Object(Mage_Core_Model_Layout_Element))
#7 /home/partmonster/public_html/app/code/core/Mage/Core/Controller/Varien/Action.php(344): Mage_Core_Model_Layout->generateBlocks()
#8 /home/partmonster/public_html/app/code/core/Mage/Core/Controller/Varien/Action.php(269): Mage_Core_Controller_Varien_Action->generateLayoutBlocks()
#9 /home/partmonster/public_html/app/code/core/Mage/Checkout/controllers/OnepageController.php(268): Mage_Core_Controller_Varien_Action->loadLayout(false)
#10 /home/partmonster/public_html/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Checkout_OnepageController->reviewAction()
#11 /home/partmonster/public_html/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('review')
#12 /home/partmonster/public_html/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#13 /home/partmonster/public_html/app/code/core/Mage/Core/Model/App.php(365): Mage_Core_Controller_Varien_Front->dispatch()
#14 /home/partmonster/public_html/app/Mage.php(683): Mage_Core_Model_App->run(Array)
#15 /home/partmonster/public_html/index.php(85): Mage::run('', 'store')
#16 {main}