This page is only relevant if you installed the 2.0.14 or 2.0.15 patch or upgrade, installed 2.0.14 or 2.0.15 directly, or installed a theme created prior to the release of 2.0.14 and started having problems with users logging into your forum. The error message which is shown will be a session timeout.
SMF 2.0.14+ now requires the a session check in the <form> for the login function. If your custom theme has a login form, such as in
index.template.php,
boardindex.template.php or
login.template.php, you will need to modify the theme to allow the login function to work correctly. In order to modify the theme, add the following code along with the other "hidden" input types, or anywhere before the closing </form> tag in the login form.
Now go to Public_html/Themes/default/Login.template.php
And add this code before </form>
<input type="hidden" name="', $context['session_var'], '" value="', $context['session_id'], '" />
Also if your theme has Login on your homepage, edit the
index.template.php, you should have:
echo '
<input type="hidden" name="hash_passwrd" value="" />
</form>';
Replace it with:
echo '
<input type="hidden" name="hash_passwrd" value="" />
<input type="hidden" name="', $context['session_var'], '" value="', $context['session_id'], '" />
</form>';
Depending on what modifications you have, you're going to want to find where there are login forms... the script change is going to be the same as above for each of them. as a for instance, that social login has it's script in a file (again IIRC) sociallogin.php... all of the login scripts need that sessions check added to them, which is generally contained to themes that you ported from versions prior to 2.0.14 or 2.0.15...
Source:
Simple machine