In one of the websites I am working on, I noticed that if I add http://www, the session_start(), won't work but if I add http:// without the "www", the session_start() will work. For example

<?php session_start();

http://www.example.com/useraccount
?>

In the above code, the session_start() won't work and the user will appear to be logout but with the code below (without the "www"), everything will be working perfectly.
<?php session_start();
http://example.com/helloworld
?>

Can someone tell me what is causing this problem?

1) What exactly are you trying to do?
2) Why is the url inside the php script block?
3) When all is said and done, you might want to look at using a 301 redirect to send all your "non-www" urls to their "www" equivalents

good luck!

yawa-ti-de:

2) Why is the url inside the php script block?

I guess it is a reference to the page contents. @poster, you probably need to give a few more details.