session loss

Hi,

I've been searching for a long time, but couldn't come up with a
solution or a clue, so I submit my case to your attention :

1. On a Windows client, an application creates a temporary htm file and
opens it with IE 6. This file only contains a redirection instruction
to an outside URL :

<META HTTP-EQUIV=Refresh
CONTENT="0;url=http:/my.url.com/?params=zdazdazda">

2. once I navigate at this adress, everything is fine until the site
opens a pop-up window, I close it _and_ try to follow another link
(still inside the site) : the client loses the session reference

On the server side, PHP based, the file containing the session data
still exists in /tmp.

What I can do :
- update the temporary htm file
- modify the php files
What I can't do :
- skip the Windows app.
- use another browser

My config :
client : WinXP SP2 + IE 6.0.2800
server : L.A.M.P.

I'd be very willing to discuss with you any solution.

Regards.

.