sessions - stop working

[Anon]

I register sessions:

session_start();
session_register("dn_ses");
$dn_ses = $dn;

Then I check if it exists:

session_start();
if (session_is_registered("dn_ses")){
} else {
do something....
}

So sometimes it works, sometimes not (I see no logical explanation - is there any bug in php sessions I should know about?).
What is wrong with that?

[junebug]

you have it a little backwards. it should look like this:

session_start();
$dn_ses = $dn;
session_register("dn_ses");

[Anon]

It did not help at all :-(
...all the time the same problem