using the login_redirect hook

[endquote]

This might be a dumb question, but here goes. I have a site which uses its own login form for the whole site, and also logs people into vB when they use that form. In cases where vB presents a login form (like if you try to post a thread or something) I want to redirect people to my form instead.

I tried putting this in the login_redirect hook, but it doesn't do anything:

exec_header_redirect("/user/login.php?referrer=%2Fvb");

The plugin system is on and this plugin is enabled, but nothing I put in there (even die()) will do anything. Am I using the wrong hook or something?