Hi Darren,

Its possible this is a timeout problem - are you running anything else which could cause this?

This maybe helpful - 

"fastcgi timeout settings the program_assignment event from instant to cron. That would make the messages send on the next cron run instead of straight away, and should stop you from timing out.

The sql statement to do that would looks something like this:
UPDATE mdl_events_handlers SET schedule = 'cron' WHERE eventname = 'program_assigned';

George.