Perl/Cookie Issues

Okay this is a tough and obscure one so I'm going to post as much background
 as I can. Even if I can't get a solution based on what I know thus far; ide
as are better than nothing. 

So here goes:

I've made a cookie-based authentication script. It's as simple as the login/
password and session ID being stored in a cookie on the user end and the aut
hentication script is executed each time data is submitted. If for some reas
on the login/pw on the user's side don't match the server side, they're boot
ed out.

For navigation I'm simply using a "session file" to determine what's display
ed on the user screen. The session file is changed depending on what's submi
tted to the main script.

IE: if the user clicks on a hyperlink that's pointing to "http://website.com
/cli/client.cgi?cmd=OPERATION&ident_a=123&ident_b=123"

I'll have the script update the session file to store what part of the site 
the user is currently visiting, and then, using SSI, send it back to the "in
dex.shtml" page where the proper results *should be* displayed. 

Okay so here's my problem:

I have a user who can connect and login to the site fine. They enter their l
ogin/pw on the form and it brings them to their member home page. However, w
henever they try to submit any further data, it doesn't update on the server
 side. It's almost like their machine wont let them submit queries with argu
ments.

I know they have cookies enabled and I know they're working because of the s
imple fact that they are able to login, and see the proper login page with t
heir info listed and such.

-ANY- comments, suggestions, or possible solutions would be much appreciated
.

If I've left anything out or if anyone needs any more info, please don't hes
itate to ask.

Thanks.