How is it possible to run the chat on www. and without the www.????

and if it's not possible to run it on both, where can i change from without to www.`?

Actually it's running only without the www.

Please help me.

yes you can!
it depends on how you load the javascript file, the script tag which you copy-pasted holds the key.
for e.g if your site is www.example.com, then the "src" in script tag must include "www"
and if your site is example.com then "src" in script tag must exclude the "www"

there are two ways you can solve this problem,
*redirect all non-www requests to your webpage to www (using htaccess or PHP)

*check whether the page loaded is www or non-www and use the script tag accordingly. (use the 'if' statement in PHP)

* there is a third way, this bug has been solved, you might want to wait for version 5.0. (will be released by the end of this month)