Joomla 3 Invalid Token error

Every time I log into joomla admin I get the following error:

The most recent request was denied because it contained an invalid security token. Please refresh the page and try again.

And the only way I can get to admin section is to go back a page or 2 and I'm in. What could be causing this really annoying behaviour?

I'm running Joomla 3.1.5 with K2.

Seems as though this question is getting a lot of views so here is the solution I came up with to handle token errors. Since seeing the error would likely mean nothing to the user, I wanted to log the user out and redirect token errors to the home page. The only way I could achieve this was with a plugin.

Credit to joomunited.com for the original token interceptor plugin which can be found here.

Here is my modified version which includes a user logout and a redirect to the homepage with a message. Hope this helps!

tokeninterceptor.php:

class PlgSystemTokeninterceptor extends JPlugin
{

    public function __construct(&$subject, $config = array())
    {
        parent::__construct($subject, $config);
        $app = JFactory::getApplication();

        if (($app->isSite() && $this->params->get('use_frontend')) || ($app->isAdmin() && $this->params->get('use_backend'))) 
        {
            register_shutdown_function(array($this,'redirectToHome'));
        }

    }

    public function redirectToHome()
    {
        $content = ob_get_contents();

        if($content == JText::_('JINVALID_TOKEN') || $content == 'Invalid Token')
        {
            $app = JFactory::getApplication();

            if (!JFactory::getUser()->guest)
            {
                $app->logout();
            }

            $app->redirect(JURI::base().'index.php?invalid_token=true');

            return false;   
        }
    }

    function onAfterInitialise()
    {
        $app = JFactory::getApplication();
        $invalid_token = $app->input->get('invalid_token', 'false');

        if ($invalid_token == 'true')
        {
            $app->enqueueMessage(JText::_('JINVALID_TOKEN'), 'warning');
        }

        return true;
    }

}