Cookie / Login issue - standard answers does not work. I will PAY you to help me fix

[602 Streets]

I develope a website, 602streets.com

On this web site, people can upload artist pages and music.

Each user can have a number of "artists" associated with their account.

I use the vBulletin user system for authentication.

So, when a user goes to the artist login page, it automatically displays their artists and lets them edit their artists, based on their vBulletin userid.

The way I do it is simple, I have a table for artists. One of the fields in this table is "ForumUserID". So whenever someone want to add or update their artists, the site simply reads the "bbuserid" cookie and checks for any matches in the artist table.

This works perfect for 90% of my users.

However, for 10% of the users, there are weird, inconsistent problems.

They will log in to vBulletin. It will show them as "logged in". It will show them as logged in accross the entire web site, including non Vbulletin pages. For example, the site home page shows if you're logged in, again based on the bbuserid cookie.
So far so good. The cookie is written and read fine and my lookups are working great. EXCEPT FOR on ONE page. for some reason, when users (about 10% of them) go to log in to their artist page, it says they are not logged in (to vbulletin).

I use the exact same method of checking if they are logged in as I do on every other non-vb page. but for some reason it does not work on this page for about 10% of my users.

I have been through the delete cookies script that was up here, it does not help. I have made sure users have cokies enabled - not the issue. I have tried to narrow it down to a browser, or OS, but there is no pattern.

The only thing I can think of is, the page in question is 1 directory deeper than the other pages. Copuld this be the issue?

1. why does it affect only some users?
2. Which users is it affecting and why?
3. how can I fix this.

PLEASE PLEASE PLEASE help me. I will pay you. I will give you logins to investigate. I just need help.

site: www.602streets.com
the page that has problems: http://www.602streets.com/Users/loginform.php

it may effect other pages in the Users folder (i.e. http://www.602streets.com/Users/ArtistAdmin2.php ) but Im not sure yet.

The problem seems to have gotten much worse with vB3. In vB2 it did happen but much less often.

Thanks in advance for anyone who can help.