OK, the code in question is:

PHP Code:
$uid = isset($_POST['uid']) ? $_POST['uid'] : $_SESSION['uid'];
$pwd = isset($_POST['pwd']) ? $_POST['pwd'] : $_SESSION['pwd']; 
Both of these ($uid and $pwd) are strings. So if I set them both to empty strings first, this problem should go away?

That seems a bit odd, seeing as the code above is setting them anyway. Or am I missing something?

Do you have to declare variables in PHP before you can use them? For example in ASP you have to use dim, and in CF you have to use <cfset>. Seems like with PHP you can just get in there and start assigning values to them