Welcome the Technical Support section. Help us in assisting you by providing us with a concise and descriptive elaboration of your issues. Be specific and if possible, provide us with a step-by-step instruction in replicating your problem.
The register page only can be used once, and cant be used from cache, since if you click back so the browser will use using cache code then. You need full refresh for making it works. This is default security from Joomla system.