PHP time out / MYSQL failure on edit Individual contact

Trying to set up a CIVICRM/Drupal 7 install to replace existing database. Installed both onto a IIS server with PHP 5.3.8 (memory 256M) and MYSQL 5.1.30.

Imported around 13,000 organizations onto the system via SQL from existing MYSQL DB without any significant errors, but then lost the ability to edit the admin individual contact record. PHP seems to kill MYSQL, resulting in the error:

"PHP Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 276481 bytes) in F:\Websites[online]\Co-operatives UK [v002]\html\sites\all\modules\civicrm\CRM\Core\Error.php on line 386"

Can still however edit organization records without problem. Can also edit the civicrm record for the admin account through the link on the drupal account edit page.

Any help on why this is happening would be much appreciated: I can only assume that saving an individual record somehow tries to pass a query of all organizations through MYSQL?