Ext No center region defined in BorderLayout

//No center region defined in BorderLayout 
var vpt = new Ext.Viewport({
                          layout:'border',
                          items:[
                              {region:"west",xtype:"panel",
                                 // layout:'border',border:false,//問題出在這裏
                                  collapsible:true,split:true,title:"操作面板",width:210,
                                  items:[tabs]
                        
                              },
                              {
                                  region:'center',
                                  xtype:'panel',
                                  contentEl:'infContent',
                                  loadMask :true,
                                  //items:[tabs]
                                   tbar:[{text:code_mean,handler:function(){}},{text:"",handler:function(){}}]
                              }]
                      });