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I get error 500 when access to your store link. The problem maybe caused by your theme miss form key in login page and register page.
You can try open 2 files:
After that, find code "<?php echo $this->getBlockHtml('formkey'); ?>" . If this files doesn't has this code, please the code: "<?php echo $this->getBlockHtml('formkey'); ?>" under form tag.