IIS5.0/PHP4.03 killing all sessions. HELP!!!!

Hi!. I have the following problem (we are going crazy about it!!) and i think there's many people out there that have experienced the same thing: A session created in one page is killed on the next one. Check an example: PAGE 1: session_start(); session_register("myvar"); $myvar="hello"; PAGE 2: session_start(); //A new session_id is generated...!! //...Instead of using the already created one...! //...Even when PHPSESSID is passed on as a get-variable!!. echo $myvar; //$myvar does not exist!!!. echo $HTTP_SESSION_VARS["myvar"]; //$HTTP_SESSION_VARS["myvar"] does not exist either!!!. Here are some configuration parameters I am using: session.use_cookies ON (I tried OFF also without success). session.auto_start OFF (I tried ON also without success). session.use_trans_sid ON (I tried OFF also without success). register_globals ON track_vars ON HERE ARE SOME CLUES: 1.The session files in the server are being written fine, their contents look fine MOST of the time, although sometimes not all session vars or values are being written or files are empty. Read and write permissions in the directory have been double checked. 2.Sometimes sessions last trough one or two pages after the first session_start(), but then they are killed on each and every page. HELP PLEASE!! Any ideas will be greatly appreciated since I've tried almost all that has come to my mind. THANKS A LOT IN ADVANCE. Cheers to everyone, Diego.