I just applied patch 6788 successfully and now I'm trying to apply patch 7405, but it gives me this error:
bash PATCH_SUPEE-7405_CE_1.9.2.1_v1.1-2016-02-23-07-42-31.sh
Checking if patch can be applied/reverted successfully...
ERROR: Patch can't be applied/reverted successfully.
patching file app/code/core/Mage/Adminhtml/Helper/Sales.php
Hunk #1 FAILED at 121.
1 out of 1 hunk FAILED -- saving rejects to file app/code/core/Mage/Adminhtml/Helper/Sales.php.rej
patching file app/code/core/Mage/Core/Model/Config.php
Hunk #1 FAILED at 1642.
1 out of 1 hunk FAILED -- saving rejects to file app/code/core/Mage/Core/Model/Config.php.rej
patching file app/code/core/Mage/Sales/Model/Quote/Item.php
Hunk #1 FAILED at 507.
1 out of 1 hunk FAILED -- saving rejects to file app/code/core/Mage/Sales/Model/Quote/Item.php.rej
patching file lib/Varien/File/Uploader.php
Hunk #1 FAILED at 216.
Hunk #2 FAILED at 538.
2 out of 2 hunks FAILED -- saving rejects to file lib/Varien/File/Uploader.php.rej
I tried replacing those files with the ones from the original Magento installation in case they were modified, but that didn't work.
How do I fix this? I'm using Magento version 1.9.2.1.
I suggest you to install 7405 without SSH and test full site.
You can download the patch from https://magentary.com/kb/install-supee-7405-without-ssh/
Make sure to keep backup of core files.
Recommend you to download fresh file app/code/core/Mage/Adminhtml/Helper/Sales.php and replace it then apply the patch. Same for other files.
That should fix the trouble.
To download your version of Magento and move fresh file on your server.