Hi,
Do you have something in the PHP error log.
This is your webserver log (apache2 I guess) and it just said that the PHP script stop working on a timeout.
So, it could be a PHP error or a real timeout (maybe some shipping plugins which make some external calls ?)
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.