Session has expired when trying to subscribe to a membership

This error message has several possible causes:

• a session handler limitation = in order to correct this please try setting the session handler option from Site > Global configuration > Session to none
• setting the membership description, emails or messages using a HTML generator(the HTML generator can add extra code that could exceed the data limit that can be stored in the database for these fields) = in order to correct this plese try clearing the membership description, emails or messages, and setting them manually from the membership configuration in your administrative panel
• 3rd party factor(system plugin, module, script loaded from your template) = to resolve this case you will need to disable the plugins and modules loaded on your membership subscription page untill the issue is resolved, then enable then one at a time in order to identify the plugin or module that affects the functionality of the subscription process
• SEF settings (depending on your SEF URLs settings or component used for this functionality, an extra redirect could be triggered on your page due to an incorrect path to an image or script, thus affection the current user session)- you can try to correct this by disabling the SEF URLs feature temporarily