[Not repeatable] js errors on login page [1.3.6]

On a clean 1.3.6 install (zen-cart-v1.3.6-full-fileset-10272006)

Firefox (2.0) Error Console complains about:

Fout: syntax error
Bronbestand: http://www.xxxx.xx/index.php?main_page=login
Regel: 37, Kolom: 4
Broncode:
} else {

Fout: update_zone is not defined
Bronbestand: http://www.xxxx.xx/index.php?main_page=login
Regel: 1

I did install a language pack, but switching back to English does not help (in the past I noticed language files sometimes cause js errors).

No idea why it happens and if it causes real problems, but I just noticed it on two fresh installs today.

I can't duplicate this. Anything special about the set up on those servers?

The actual URL or a copy of the View Source content from the page would be helpful ...

Yes I understand, I assumed it would be the same with any fresh install, but appearantly it's not.

The sites aren't clean anymore now, and I rather do not post the url's, sorry about that. But I will keep an eye on it and post an url/code if it happens again on another fresh install.

(And I suppose it was clear but I meant to say: the Javascipt error console)

Anything special about the set up on those servers?Not that I am aware of.

I will post back later if it happens again, and post more info then.