'null' is null or not an object

Server: Ubuntu, 2.6.22.13-0.1
Client: MS Windows, Vista SP1
Browsers: IE7 and Firefox 3
Version: 5.x-1.1b

On this version and RC4, when a page with a chat displays, there are always errors on the page. Or rather a single error: 'null' is null or not an object. According to the Firefox pluging, Firebug, this is coming from Lightbox2. When I disable Lightbox2 for pages that use phpfreechat, I get a different, single error: '$.browser.msie' is null or not an object. Firebug says this is from panels.js. It looks like both of these are happening because of "handler.php?pfc_ajax=1&f=loadChat" and prototype.js (line 1223).

I know nothing about javascript, and could use some help with this. One more thing, the server, Ubuntu, is a virtual machine running on vmware. I was using vmware server 2,0 RC1, but have switche to vmware player 2.5, as it uses fewer resources.

Below are my debug parameters:

Parameters: Array
(
[data_private_path] => /srv/www/html/files/phpfreechat/private
[data_public_url] => http://www.djfgtvcbd.com/files/phpfreechat/public
[data_public_path] => /srv/www/html/files/phpfreechat/public
[theme_url] => http://www.djfgtvcbd.com/sites/default/modules/phpfreechat/extras/themes
[theme_path] => /srv/www/html/sites/default/modules/phpfreechat/extras/themes
[theme] => drupal
[server_script_url] => http://www.djfgtvcbd.com/sites/default/modules/phpfreechat/handler.php
[server_script_path] => /srv/www/html/sites/default/modules/phpfreechat/handler.php
[language] => en_US
[frozen_nick] => 1
[isadmin] => 1
[firstisadmin] =>
[islocked] =>
[quit_on_closedwindow] =>
[focus_on_connect] => 1
[connect_at_startup] => 1
[start_minimized] =>
[nickmarker] => 1
[clock] => 1
[startwithsound] => 1
[openlinknewwindow] => 1
[notify_window] => 1
[short_url] => 1
[display_ping] => 1
[display_pfc_logo] => 1
[displaytabimage] => 1
[displaytabclosebutton] => 1
[showwhosonline] => 1
[showsmileys] => 1
[btn_sh_whosonline] => 1
[btn_sh_smileys] => 1
[debug] =>
[get_ip_from_xforwardedfor] =>
[nick] => kenbradford
[serverid] => 2bd0a9380d15fee8aacd1d9fd3f49938
[title] => Demo Chat 4
[channels] => Array
(
[0] => Demo Chat 4
)

[nickmeta] => Array
(
[drupal_base_url] => http://www.djfgtvcbd.com
[drupal_user_uid] => 1
)

)

Thanks.