I am also facing the same issues after upgrading the magento version from version 1.9.2 to version 1.9.3.6 ...pages simply show flas.. your help would be much appreciable.
Thanks
Here is my Code for the registration:
<form action="https://www.my-example.com/customer/account/createpost/" method="post" id="form-validate">
<div class="fieldset">
<input type="hidden" name="success_url" value="">
<input type="hidden" name="error_url" value="">
<input type="hidden" name="form_key" value="w5aGzmiwvqzKXllY">
<h2 class="legend">Daten Ansprechpartner</h2>
<ul class="form-list">
<li class="fields">
In your code it is missing:
<form action="http://your-example.com/customer/account/createpost/?SID=91i3p974p1jtggdljian86v925" method="post" id="form-validate" class="register-form">
<div class="fieldset">
<input type="hidden" name="success_url" value="">
<input type="hidden" name="error_url" value="">
<h2 class="legend">Personal Information</h2>
<ul class="form-list">
<li class="fields">
<div class="customer-name-middlename">
<div class="field name-firstname">
I find the formkey for the login but not for registration. Try to find the right path for the .phtml with the simlinks.
Have you editet the register.phtml formkey? (In your custom template) If it is so here is a way to solve the problem: https://community.magento.com/t5/Technical-Issues/Customer-Registration-not-working-in-1-9-2-2/td-p/20563