It's that one:
[Thu Mar 21 07:34:58 2013] [error] [client 178.59.197.244] PHP Fatal error: Allowed memory size of 343932928 bytes exhausted (tried to allocate 8388608 bytes) in /home/ubookftp/www.ubook.gr/libraries/joomla/database/database/mysql.php on line 712, referer:
ubook.gr/administrator/index.php?option=...ikashop&ctrl=product
So it means that the memory is getting filled completely before it can display anything.
So it's not an error, just that the data is too much to handle.
Maybe some kind of optimization in HikaShop could be possible but we won't be able to look at that before next week.
Is that a brand new install of HikaShop 2.1.1 or was it updated from a previous version ? With the 2.1.1, if you have a fresh install, you have improvments in the database to optimize queries for lot of data like here. Maybe that could help ?
Actually, we've only added some strategic indexes in some tables. That would already be a good start I think. You can compare the back/tables.sql file of the install package with the tables structure on your website to add the indexes if it's not a fresh install of the latest version and thus get these improvements.