I get Fatal Error in a Block

Hi,

i get the following Fatal Error, when i integrate a chatroom in a block (on my Testserver with Lamp):

Fatal error: Call to undefined function chatroom_chat() in /opt/lampp/htdocs/drupal/includes/common.inc(1547) : eval()'d code on line 1

i used the following php code in the block:

<? print chatroom_chat(1);?>

On your testserver it works. I use drupal 6.6.

Greetings

strauch