updating PHP problem

I've installed PHP 4.3.6 on my laptop.

My dev machine is on PHP 4.3.3

Since, some lines doesn't work anymore:
2: header("Cache-Control: max-age=" . $this->allowcache_expire * 60);

gives me those errors:
Notice: Undefined variable: this in
c:\inetpub\wwwroot\Connections\config.php on line 2

Warning: Cannot modify header information - headers already sent by (output
started at c:\inetpub\wwwroot\Connections\config.php:8) in
c:\inetpub\wwwroot\Connections\config.php on line 2

Warning: session_start(): Cannot send session cookie - headers already sent
by (output started at c:\inetpub\wwwroot\Connections\config.php:8) in
c:\inetpub\wwwroot\default.php on line 3

Warning: session_start(): Cannot send session cache limiter - headers
already sent (output started at c:\inetpub\wwwroot\Connections\config.php:8)
in c:\inetpub\wwwroot\default.php on line 3


also those line:
3: session_start();
4: if ($_SESSION["UID"] != "") {
5: $UserID = $_SESSION["UID"];
6: }
this line gives me this error:
Notice: Undefined index: UID in c:\inetpub\wwwroot\default.php on line 4

The same code on the PHP 4.3.3 works just fine.

WHAT I'M MISSING ???

Bob