You can activate the debug for the siteaccess you would like to do this override.
Tick the list of templates to view what templates are loaded. You will see if your template is loaded.
Yes, I have cleaned the cache. And in the debug output it is loading the correct template i.e register_over.tpl.
Even i have removed the overriden template and check the /user/register.tpl but i has also the same problem. I think the attributes fetching section is not working properly.
This template is doing exactly what you said : it's looping on a new user attributes.
Check your user class for an an attribute type called User Account. If this one is not present you won't be able to login in eZ.