I've done a bunch of work with codeigniter, cakephp, zend, magento and they all have methods for setting what I've heard called flashdata errors.
see:
- http://inchoo.net/ecommerce/magento/magento-frontend/utilizing-magento-notification-system/
- http://ellislab.com/codeigniter/user-guide/libraries/sessions.html
This is basically a value set in session that every page looks for and if found displays then clears from the session so that it is only displayed once.
Typically these are displayed in the form of a popup or small short lived box that is color coded depending on the level.
Ex: message : blue success : green warning : yellow error : red
Is there something like this within wordpress where you can for instance do some business logic through a post to say "wp_ajax" or "wp_ajax_nonpriv" and if something breaks redirect to the previous page after adding a flash data error?