I tried to load CKEDITOR in a jquery tab via ajax. I got problem that only first time the ckeditor is working but when I click on other tab and again got o ckeditor tab its not working. in Load section for tab I put the following code.

load: function(event, ui) {
  if(ui.index == 3){ // Checked tab no 4
    var instance = CKEDITOR.instances['reditor']; // reditor is text area id, check if instances exists for readitor or not 
    if(instance){ 
       CKEDITOR.remove(instance); //if existed then remove it
    }
    CKEDITOR.replace( 'reditor' ); // Create instance for 'reditor'
 }
}

in this way we can get rid the problem of “CKEditor instance already exists”

Here is whole configuration

$(document).ready(function () {
           var $tabs = $("#tabs").tabs({ 
                                
                                alignment: "top",
                                spinner : false,
                                ajaxOptions: {
                                    error: function( xhr, status, index, anchor ) {
                                                    $( anchor.hash ).html( "Couldn't load this tab. Please try again.");
                                                },
                                    complete: function(){
                                        
                                        
                                    }
                                    
                                },
                                load: function(event, ui) {
                                    if(ui.index == 3){
                                        var instance = CKEDITOR.instances['reditor'];
                                        if(instance){
                                            CKEDITOR.remove(instance);
                                        }
                                    }
                                },
                                select: function(e, ui){
                                            $(ui.panel).html('<img src="img/ajax_loader.gif" />'); // Loader after click on each tab
                                        }
                                
                                });
           $tabs.tabs('select', <?=$tab_no?>); // used for selected default tab
           
        });
        

Here is HTML/PHP (I used cakephp syntax for url ) used “TEXT” in a link to show the loading text on tab otherwise it will not show the loading tabl

<div id="tabs">
    <ul>
        <li>
            <?=$html->link("<span>Information</span>", array("controller" => "listings", "action" => "information", $id), array("escape" => false, "title" => "Information"))?>
            
        </li>
        <li>
            <?=$html->link("<span>Detail</span>", array("controller" => "listings", "action" => "detail", $id), array("escape" => false))?>
        </li>
        <li>
            <?=$html->link("<span>Peoples</span>", array("controller" => "listing", "action" => "peoples", $id), array("escape" => false))?>
        </li>
        <li>
            <?=$html->link("<span>Enhance</span>", array("controller" => "listings", "action" => "enhance", $id), array("escape" => false))?>
       </li>
    </ul>
 </div>

In this way I did and it work for me 🙂