Error 500 when testing, but the site is working fine

[almarma]

Hello everybody,

I use to check my websites with WebPageTest quite often, to check if everything is working fine. I never had problems with Wordpress sites I run, but the Prestashop site I created is driving me crazy.

The site is at http://www.nordicvapor.com

While it's working fine, and customers are buying, when I try to test the performance, very often (not always) I get Error 500 results like this one from today:
http://www.webpagetest.org/result/131205_E0_M4V/

As far as I know, the site is performing well for humans, but WPT doesn't seem to like the site.

I the site I have a plugin that redirects the user to a specific domain, depending on the browser language. Maybe that's the problem? I'm trying to avoid it adding the /en/ folder for English language, but the problem is still there. Any clue? Is anything wrong with my site?

Thanks in advance!

[robzilla]

I get a 500 error, too, when I go to that URL (from the Netherlands), but from the Kansas City test location, it does seem to be working: http://www.webpagetest.org/result/131205_19_TXJ/

The Kansas City location connected to 108.162.196.50 while one in Israel connects to 108.162.197.50 and gets a 500 error (this is also the IP where I end up, probably the Amsterdam node). Have you tried temporarily disabling CloudFlare?

By the way, judging from the above test results, you have some odd redirects:
[http://www.nordicvapor.com/] 301 >
[http://www.nordicvapor.com/en/] 302 >
[http://www.nordicvapor.com/en/?redirected] 301 >
[http://www.nordicvapor.com/en/]

[lupinehorror]

just to add to this...your site just displays a blank page in my browser (currently win7 - firefox 25 and chrome 33) with javascript off or javascript on. i've been directed to http://www.nordicvapor.com/en/
it seems to display alright from denver... http://www.webpagetest.org/result/131206...1/details/ though you've got one 404 error showing.

[robzilla]

The error page is indeed a blank one, the 500 status code is returned in the headers.

Interestingly, Denver connects to 108.162.197.50, the IP that previously gave me (and the Israel location) the 500 error.

@almarma: are you doing any geotargeting or load balancing?