I have tried to upgrade magento (1.7.x to 1.9.x) twice and the first time it seemed to work fine for 1 day then it some how reverted it self the 1.7.x. the Second time It worked okay, but customers couldnt log in!
So what am I missing....
Can I upgrade Magento using Magento Connect?
There is a problem with the form key. Please place the below code in all phtml files which contains form tag.
<?php echo $this->getBlockHtml('formkey') ?>