To me it looks like the patch was not installed properly.

The validateFormKey function is included in the patch.

• Open the app/code/core/Mage/Core/Model/Session.php file and double check if the validateFormKey function is here

• If the file is overridden in app/code/local/Mage/Core/Model/Session.php, you have to add the new methods validateFormKey and renewFormKey manually in the overridden file. Also change line 60 from:

       $this->setData('_form_key', Mage::helper('core')->getRandomString(16));
  

  to

       $this->renewFormKey();
  

• If it's here, it's definitely a caching/compilation problem. Flush your cache, as well as any other cache (Varnish / APC etc...)

• If you have compilation enable, please disable compilation then recompile.

• If the function is not here, that means the files have not been uploaded properly. Please note that when you extract the archive from Magentary, the files are extracted in a SUPEE-7405-1.9.2.1 folder, you must open this folder and extract the files from this folder to your Magento root, transfering the entire SUPEE-7405-1.9.2.1 folder will not apply the patch.

To me it looks like the patch was not installed properly.

The validateFormKey function is included in the patch.

• Open the app/code/core/Mage/Core/Model/Session.php file and double check if the validateFormKey function is here

• If the file is overridden in app/code/local/Mage/Core/Model/Session.php, you have to add the new methods validateFormKey and renewFormKey manually in the overridden file. Also change line 60 from:

   $this->setData('_form_key', Mage::helper('core')->getRandomString(16));
  

  to

   $this->renewFormKey();
  

• If it's here, it's definitely a caching/compilation problem. Flush your cache, as well as any other cache (Varnish / APC etc...)

• If you have compilation enable, please disable compilation then recompile.

• If the function is not here, that means the files have not been uploaded properly. Please note that when you extract the archive from Magentary, the files are extracted in a SUPEE-7405-1.9.2.1 folder, you must open this folder and extract the files from this folder to your Magento root, transfering the entire SUPEE-7405-1.9.2.1 folder will not apply the patch.

To me it looks like the patch was not installed properly.

The validateFormKey function is included in the patch.

• Open the app/code/core/Mage/Core/Model/Session.php file and double check if the validateFormKey function is here
• If it's here, it's definitely a caching/compilation problem. Flush your cache, as well as any other cache (Varnish / APC etc...)
• If you have compilation enable, please disable compilation then recompile.
• If the function is not here, that means the files have not been uploaded properly. Please note that when you extract the archive from Magentary, the files are extracted in a SUPEE-7405-1.9.2.1 folder, you must open this folder and extract the files from this folder to your Magento root, transfering the entire SUPEE-7405-1.9.2.1 folder will not apply the patch.

To me it looks like the patch was not installed properly.

The validateFormKey function is included in the patch.

• Open the app/code/core/Mage/Core/Model/Session.php file and double check if the validateFormKey function is here

• If the file is overridden in app/code/local/Mage/Core/Model/Session.php, you have to add the new methods validateFormKey and renewFormKey manually in the overridden file. Also change line 60 from:

       $this->setData('_form_key', Mage::helper('core')->getRandomString(16));
  

  to

       $this->renewFormKey();
  

• If it's here, it's definitely a caching/compilation problem. Flush your cache, as well as any other cache (Varnish / APC etc...)

• If you have compilation enable, please disable compilation then recompile.

• If the function is not here, that means the files have not been uploaded properly. Please note that when you extract the archive from Magentary, the files are extracted in a SUPEE-7405-1.9.2.1 folder, you must open this folder and extract the files from this folder to your Magento root, transfering the entire SUPEE-7405-1.9.2.1 folder will not apply the patch.