Warning when installing any plugins

Hi all, I tried to install CKEditor in modx manager, but everytime I try to save always appear a warning like this:

Warning: stripslashes() expects parameter 1 to be string, array given in /home/bedo/public_html/manager/index.php on line 7

Warning: Cannot modify header information - headers already sent by (output started at /home/bedo/public_html/manager/index.php:7) in /home/bedo/public_html/manager/index.php on line 70

Warning: Cannot modify header information - headers already sent by (output started at /home/bedo/public_html/manager/index.php:7) in /home/bedo/public_html/manager/index.php on line 71

Warning: Cannot modify header information - headers already sent by (output started at /home/bedo/public_html/manager/index.php:7) in /home/bedo/public_html/manager/index.php on line 72

Warning: Cannot modify header information - headers already sent by (output started at /home/bedo/public_html/manager/index.php:7) in /home/bedo/public_html/manager/index.php on line 73

Warning: Cannot modify header information - headers already sent by (output started at /home/bedo/public_html/manager/index.php:7) in /home/bedo/public_html/manager/index.php on line 74

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/bedo/public_html/manager/index.php:7) in /home/bedo/public_html/manager/includes/config.inc.php on line 60

Warning: Cannot modify header information - headers already sent by (output started at /home/bedo/public_html/manager/index.php:7) in /home/bedo/public_html/manager/includes/config.inc.php on line 74

Warning: Cannot modify header information - headers already sent by (output started at /home/bedo/public_html/manager/index.php:7) in /home/bedo/public_html/manager/index.php on line 176

Warning: Cannot modify header information - headers already sent by (output started at /home/bedo/public_html/manager/index.php:7) in /home/bedo/public_html/manager/processors/save_plugin.processor.php on line 153

What’s is really happen???

The first error is important:


The rest are caused by that first error. Can you describe how you are installing this plugin?

I just follow the steps what http://codingpad.maryspad.com/2010/02/21/setting-up-ckeditor-on-modx-evolution/ said:

Installing the Plugin

• Inside the assets->plugins folder of your extracted folder is the ckeditor folder. Move this to the plugins folder on your MODx site (assets->plugins).
• Go into Elements->Manage Elements->Plugins, and create a new plugin called ckeditor. Copy the contents of the plugin.ckeditor.tpl file to it.
• Next, while still on the plugin code page, click on the System Events tab and check the following events: OnRichTextEditorInit, OnRichTextEditorRegister, and OnInterfaceSettingsRender
  

But after I followed the third step, that warning appear.

so this error came up BEFORE you even saved your plugin?