Plugin does not have a valid header

I have tried to upgrade to version 3.2. However, when I am asked to activate the plugin, I get the error message "The plugin does not have a valid header". When I return to the PlugIn page, there is no entry for this plugin. I have done a Google search, and here, but cannot find a solution. I have tried copying ckeditor.php from /public_html/wp-content/plugins/ckeditor/ to /public_html/wp-content/plugins/ but made no difference.

Any assistance please!
Harris