[AndrewD]

Originally Posted by Phalynx

That's the value:
error_reporting = E_ALL & ~E_NOTICE & ~E_STRICT

The blank screen and the large number of downloads are clues. I guess that your server is running out of some form of resource - memory or more likely cpu.

By default, vbulletin is not very user friendly with system errors, because of its default 'gzipping' of messages to the user. Have you tried turning off this option? vb/admin/options/cookies and http header options/ set gzip html output to 'no' and save. Then repeat the test and see if you get a message instead of a blank screen.

I'll take a look at the code to see if I can improve efficiency.

Edited: I'm pretty certain that your problem will be that the script is running out of its allowed cpu time. This is because separate email messages are being sent to each person who has accessed the entry. Grouping these messages (i.e. having multiple email addresses as 'bcc' recipients) may be a solution, but this isn't a trivial change to the code and the php documentation is not very clear on what is allowed and what is not allowed.