I have zp 1.3 and the register_user plugin installed.
After I click submit I get this error.

Call to undefined method Zenphoto_Administrator:etAlbums() in /home/gsrfanco/public_html/pennyandsheldon/photos/zp-core/zp-extensions/register_user.php on line 219

This has been fixed in the nightly builds as of changeset 5474.

I almost had the same thing happen to me but a quick refresh helped

The quick refresh also helped me with this issue. I would suggest going that route first. Thanks!