I looked into the code and found the error $forumName variable is not used properly..
In the /wp-contents/plugins/buddypress-ajax-chat/bp-chat.php
It worked when I replaced line 341-342
echo __('<p>Notice a popup window will try to appear.<br /> If you are using I.E. you might need to hold down the CTRL key when clicking on chat to allow the popup screen to appear.</p><p>If all else fails you can <a target=\'_new\' href="', 'bp-chat'); echo get_bloginfo('wpurl') . "/wp-content/plugins/buddypress-ajax-chat/bp-chat/chat/index.php?channel=$forumName"; echo __('> click here</a> for a new chat window.', 'bp-chat');
echo "<script>window.open('" . get_bloginfo('wpurl') . "/wp-content/plugins/buddypress-ajax-chat/bp-chat/chat/index.php?channel=$forumName" . "', 'BuddypressAjaxChat', 'menubar=no,resizable=no,status=no,toolbar=no,location=no,directories=no,height=600,width=700');</script>";
to this,
echo "<p>Notice a popup window will try to appear.<br /> If you are using I.E. you might need to hold down the CTRL key when clicking on chat to allow the popup screen to appear.</p><p>If all else fails you can <a target='_new' href=" . get_bloginfo('wpurl') . "/wp-content/plugins/buddypress-ajax-chat/bp-chat/chat/index.php?channel=".$forumName."> click here</a> for a new chat window.";
echo "<script>window.open('" . get_bloginfo('wpurl') . "/wp-content/plugins/buddypress-ajax-chat/bp-chat/chat/index.php?channel=".$forumName."', 'BuddypressAjaxChat', 'menubar=no,resizable=no,status=no,toolbar=no,location=no,directories=no,height=600,width=700');</script>";