Thread Prefix Error Question

[MikQuattro]

A script I use on my forum conflicts with the Thread Prefix feature in a weird way, and I'm hoping someone here can help or point me in the right direction. My script sends the user to a form when they click New Thread so they can fill in some required data. That form then dumps that data into the message area of the New Thread Editor, where the user can add to the post and then click on Submit Thread as normal.

The problem is I wish to make the Thread Prefix feature mandatory, but when I do that, and the user forgets to choose a prefix and then clicks on Submit Thread, it sends the user back to New Thread Editor page, which triggers my script and places the user back at the beginning, which is very bad.

Normally (without my script), that page would reload with an error message at the top saying "You must select a thread prefix." Which, BTW, I don't understand because if you forget to add a subject or a message, a popup pops up with the error message instead of reloading the page. But anyway, that's just me whining...

So what I want to do is change that. Instead of reloading the page with the error message, if a user forgets to choose a thread prefix, I want a popup to pop up with the message. The trouble is, I cannot find where to make these changes. I've been all over the js files and newthread.php file. Can anyone please help me?

Cheers,

--Mik