We've got a 4.6.10 CiviCRM site which has been running without fuss for a while. Now, when adding an event participant, we get an error 500. The process of adding the participant works fine (they appear in the list of participants) but the receipt does not get sent out and the page never returns. In the Apache error log, I see the following :
Allowed memory size of 536870912 bytes exhausted (tried to allocate 474218496 bytes) in /var/www/html/sites/all/modules/civicrm/CRM/Core/Error.php on line 550
The memory limit was actually 128M but it was increased, just in case. As you might guess, it makes no difference. I decided to set "display_errors = 1" in my php.ini, but that just gives me a completely white screen without the 500 error displayed.
Any thoughts or ideas on how to figure this one out would be greatly appreciated.