Checkout times out with error

-- url of the page with the problem -- : emotorwerks.com/products/online-store
-- HikaShop version -- : 2.1.0
-- Joomla version -- : 2.5,11
-- PHP version -- : where do I find that?
-- Browser(s) name and version -- : Opera 16.0.1196.73 Windows 7 64-bit
-- Error-message(debug-mod must be tuned on) -- : (in browser) Server error
The website encountered an error while retrieving emotorwerks.com/products/online-store/checkout . It may be down for maintenance or configured incorrectly.

Hi, this appeared in the last couple of days, the site was working fine before. The only thing changed on the server in this period was expansion of the partition on which our site resides (hosted on a 1and1 Cloud Server) from 4 GB to 14GB. This did not have effect on any other aspect of our site operation. I do not know if this has caused the issue in the subject but this was the only change in server config so I thought I'd report it here.

Our store is down until this is fixed - please help.

Thanks,
Valery

Thanks nicolas - here's what I see in the log file:

[Mon Nov 11 13:04:55 2013] [error] [client 72.28.152.198] PHP Notice: Trying to get property of non-object in /var/www/vhosts/default/htdocs/plugins/hikashopshipping/usps/usps.php on line 224, referer: emotorwerks.com/products/online-store
[Mon Nov 11 13:04:55 2013] [error] [client 72.28.152.198] PHP Notice: Trying to get property of non-object in /var/www/vhosts/default/htdocs/plugins/hikashopshipping/usps/usps.php on line 231, referer: emotorwerks.com/products/online-store
[Mon Nov 11 13:04:55 2013] [error] [client 72.28.152.198] PHP Notice: Trying to get property of non-object in /var/www/vhosts/default/htdocs/plugins/hikashopshipping/usps/usps.php on line 231, referer: emotorwerks.com/products/online-store
[Mon Nov 11 13:04:55 2013] [error] [client 72.28.152.198] PHP Fatal error: Call to a member function xpath() on a non-object in /var/www/vhosts/default/htdocs/plugins/hikashopshipping/usps/usps.php on line 239, referer: emotorwerks.com/products/online-store

so disabling usps plugin eliminates the error. unfortunately, along with our ability to ship with USPS (critical for international customers). Could there be a problem on USPS side changing some return data resulting in this error? We have not changed anything on the site to result in this error...

This is what we have in usps.php:

---

//Parse Domestic Response
$rateResult = $response_xml->xpath('Package/Postage'); <

---

THIS IS LINE 249 FROM THE LOGS ABOVE
$usps_rate_arr = xml2array($rateResult);
foreach($usps_rate_arr as $k=>$v) {
$usps_rates = array("Service" => html_entity_decode($v), "Rate" => $v['Ra\
te']);

---

looks like USPS request 20 lines prior fails:

---

$response_xml = $this->doUSPS($request, true);

---

??

What to do?

ok thanks, will monitor that thread. as far as I could tell, it's still not resolved, correct?