phpfreechat fails to load in IE7

I installed phpfreechat on drupal ceter 5.7 (german).
While it is working fine in Firefox 2.0 the chat does not load in IE7. Even worse the user seems to get logged out from the site, log in box is shown. After using a link to another page on the same site, the current user is shown as logged in twice or more times. Changing security settings does not seem to have impact on the problem.

The CMS is installed on a Linux/Apache Webserver running php5. Should not be a problem there since it is working fine in Firefox.
IE shows the following message in error-window:

Line: 291
Char: 2
Error: Object expected
Code: 0

Line: 259
Char: 3
Error: pfcClient is missing
Code: 0

phpfreechat debug output is:
Parameters: Array
(
[data_private_path] => /mnt/web2/12/35/5787035/htdocs/drupal-5.7/files/phpfreechat/private
[data_public_url] => http://www.zauberdose.de/files/phpfreechat/public
[data_public_path] => /mnt/web2/12/35/5787035/htdocs/drupal-5.7/files/phpfreechat/public
[theme_url] => http://www.zauberdose.de/modules/phpfreechat/extras/themes
[theme_path] => /mnt/web2/12/35/5787035/htdocs/drupal-5.7/modules/phpfreechat/extras/themes
[theme] => drupal
[serverid] => 40e5929765ec9fb44010c118e5e831c3
[server_script_url] => http://www.zauberdose.de/modules/phpfreechat/handler.php
[server_script_path] => /mnt/web2/12/35/5787035/htdocs/drupal-5.7/modules/phpfreechat/handler.php
[title] => Gildenchat
[frozen_nick] => 1
[connect_at_startup] => 1
[start_minimized] =>
[height] => 400px
[shownotice] => 2
[nickmarker] => 1
[clock] => 1
[openlinknewwindow] => 1
[showwhosonline] => 1
[showsmileys] => 1
[btn_sh_whosonline] => 1
[btn_sh_smileys] => 1
[language] => de_DE-informal
[debug] =>
[channels] => Array
(
[0] => Gildenchat
)

[nick] => Bernd
[isadmin] => 1
[nickmeta] => Array
(
[drupal_base_url] => http://www.zauberdose.de
[drupal_user_uid] => 1
)

)
Session: Array
(
[drupal_user] => stdClass Object
(
[uid] => 1
[name] => Bernd
[pass] => dfdcd2c457b484cf9814c05d523ac805
[mail] => mail@sven-peetz.de
[mode] => 0
[sort] => 0
[threshold] => 0
[theme] =>
[signature] => . ... --. .-. ..- . ... ... - -.. .. . .-- .. .-.. -.. . --. .. .-.. -.. . !
[created] => 1208086625
[access] => 1208303700
[login] => 1208303011
[status] => 1
[timezone] => 7200
[language] => de
[picture] => files/pictures/picture-1.jpg
[init] => sven@metawebdesign.de
[data] => a:3:{s:7:"contact";i:0;s:14:"picture_delete";s:0:"";s:14:"picture_upload";s:0:"";}
[sid] => sjcu3ef0dq7t3t4ip45l5ps047
[hostname] => 85.179.83.178
[timestamp] => 1208303700
[cache] => 0
[session] => drupal_user|O:8:"stdClass":27:{s:3:"uid";s:1:"1";s:4:"name";s:5:"Bernd";s:4:"pass";s:32:"dfdcd2c457b484cf9814c05d523ac805";s:4:"mail";s:18:"mail@sven-peetz.de";s:4:"mode";s:1:"0";s:4:"sort";s:1:"0";s:9:"threshold";s:1:"0";s:5:"theme";s:0:"";s:9:"signature";s:84:". ... --. .-. ..- . ... ... - -.. .. . .-- .. .-.. -.. . --. .. .-.. -.. . !";s:7:"created";s:10:"1208086625";s:6:"access";s:10:"1208303638";s:5:"login";s:10:"1208303011";s:6:"status";s:1:"1";s:8:"timezone";s:4:"7200";s:8:"language";s:2:"de";s:7:"picture";s:28:"files/pictures/picture-1.jpg";s:4:"init";s:21:"sven@metawebdesign.de";s:4:"data";s:82:"a:3:{s:7:"contact";i:0;s:14:"picture_delete";s:0:"";s:14:"picture_upload";s:0:"";}";s:3:"sid";s:26:"sjcu3ef0dq7t3t4ip45l5ps047";s:8:"hostname";s:13:"85.179.83.178";s:9:"timestamp";s:10:"1208303638";s:5:"cache";s:1:"0";s:7:"session";s:2451:"drupal_user|O:8:"stdClass":27:{s:3:"uid";s:1:"1";s:4:"name";s:5:"Bernd";s:4:"pass";s:32:"dfdcd2c457b484cf9814c05d523ac805";s:4:"mail";s:18:"mail@sven-peetz.de";s:4:"mode";s:1:"0";s:4:"sort";s:1:"0";s:9:"threshold";s:1:"0";s:5:"theme";s:0:"";s:9:"signature";s:84:". ... --. .-. ..- . ... ... - -.. .. . .-- .. .-.. -.. . --. .. .-.. -.. . !";s:7:"created";s:10:"1208086625";s:6:"access";s:10:"1208303035";s:5:"login";s:10:"1208303011";s:6:"status";s:1:"1";s:8:"timezone";s:4:"7200";s:8:"language";s:2:"de";s:7:"picture";s:28:"files/pictures/picture-1.jpg";s:4:"init";s:21:"sven@metawebdesign.de";s:4:"data";s:82:"a:3:{s:7:"contact";i:0;s:14:"picture_delete";s:0:"";s:14:"picture_upload";s:0:"";}";s:3:"sid";s:26:"sjcu3ef0dq7t3t4ip45l5ps047";s:8:"hostname";s:13:"85.179.83.178";s:9:"timestamp";s:10:"1208303035";s:5:"cache";s:1:"0";s:7:"session";s:1224:"drupal_user|O:8:"stdClass":27:{s:3:"uid";s:1:"1";s:4:"name";s:5:"Bernd";s:4:"pass";s:32:"dfdcd2c457b484cf9814c05d523ac805";s:4:"mail";s:18:"mail@sven-peetz.de";s:4:"mode";s:1:"0";s:4:"sort";s:1:"0";s:9:"threshold";s:1:"0";s:5:"theme";s:0:"";s:9:"signature";s:84:". ... --. .-. ..- . ... ... - -.. .. . .-- .. .-.. -.. . --. .. .-.. -.. . !";s:7:"created";s:10:"1208086625";s:6:"access";s:10:"1208303017";s:5:"login";s:10:"1208303011";s:6:"status";s:1:"1";s:8:"timezone";s:4:"7200";s:8:"language";s:2:"de";s:7:"picture";s:28:"files/pictures/picture-1.jpg";s:4:"init";s:21:"sven@metawebdesign.de";s:4:"data";s:82:"a:3:{s:7:"contact";i:0;s:14:"picture_delete";s:0:"";s:14:"picture_upload";s:0:"";}";s:3:"sid";s:26:"sjcu3ef0dq7t3t4ip45l5ps047";s:8:"hostname";s:13:"85.179.83.178";s:9:"timestamp";s:10:"1208303017";s:5:"cache";s:1:"0";s:7:"session";s:0:"";s:7:"contact";i:0;s:14:"picture_delete";s:0:"";s:14:"picture_upload";s:0:"";s:5:"roles";a:1:{i:2;s:18:"authenticated user";}}pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_nick|s:0:"";pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_active|b:0;pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_channels|a:0:{}pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_privmsg|a:0:{}";s:7:"contact";i:0;s:14:"picture_delete";s:0:"";s:14:"picture_upload";s:0:"";s:5:"roles";a:1:{i:2;s:18:"authenticated user";}}pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_nick|s:0:"";pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_active|b:0;pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_channels|a:0:{}pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_privmsg|a:0:{}";s:7:"contact";i:0;s:14:"picture_delete";s:0:"";s:14:"picture_upload";s:0:"";s:5:"roles";a:1:{i:2;s:18:"authenticated user";}}pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_nick|s:0:"";pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_active|b:0;pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_channels|a:0:{}pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_privmsg|a:0:{}
[contact] => 0
[picture_delete] =>
[picture_upload] =>
[roles] => Array
(
[2] => authenticated user
)

)

[pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_nick] =>
[pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_active] =>
[pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_channels] => Array
(
)

[pfcuserconfig_40e5929765ec9fb44010c118e5e831c3_privmsg] => Array
(
)

)
Cookies: Array
(
[SESS136c5c23c27e4a149e8e659ac50a4f78] => sjcu3ef0dq7t3t4ip45l5ps047
[phpfreechat] => hu7he6juk49gc254in9rg4lof1
)