When clicking on the categories (e.g. start events) in the palette on the left, the categories do not open, so it's impossible to select one of the elements inside.

The java script console shows following error message if I click on the category:
SCRIPT5007: Unable to get property 'ui' of undefined or null reference
ext-all.js, line 100, character 2113.

This is line 100, character 2113 is "A.ui.ecClick(B)".

Ext.tree.TreeEventModel=function(A){this.tree=A;this.tree.on("render",this.initEvents,this)};Ext.tree.TreeEventModel.prototype={initEvents:function(){var A=this.tree.getTreeEl();A.on("click",this.delegateClick,this);if(this.tree.trackMouseOver!==false){A.on("mouseover",this.delegateOver,this);A.on("mouseout",this.delegateOut,this)}A.on("dblclick",this.delegateDblClick,this);A.on("contextmenu",this.delegateContextMenu,this)},getNode:function(B){var A;if(A=B.getTarget(".x-tree-node-el",10)){var C=Ext.fly(A,"_treeEvents").getAttributeNS("ext","tree-node-id");if(C){return this.tree.getNodeById(C)}}return null},getNodeTarget:function(B){var A=B.getTarget(".x-tree-node-icon",1);if(!A){A=B.getTarget(".x-tree-node-el",6)}return A},delegateOut:function(B,A){if(!this.beforeEvent(B)){return }if(B.getTarget(".x-tree-ec-icon",1)){var C=this.getNode(B);this.onIconOut(B,C);if(C==this.lastEcOver){delete this.lastEcOver}}if((A=this.getNodeTarget(B))&&!B.within(A,true)){this.onNodeOut(B,this.getNode(B))}},delegateOver:function(B,A){if(!this.beforeEvent(B)){return }if(this.lastEcOver){this.onIconOut(B,this.lastEcOver);delete this.lastEcOver}if(B.getTarget(".x-tree-ec-icon",1)){this.lastEcOver=this.getNode(B);this.onIconOver(B,this.lastEcOver)}if(A=this.getNodeTarget(B)){this.onNodeOver(B,this.getNode(B))}},delegateClick:function(B,A){if(!this.beforeEvent(B)){return }if(B.getTarget("input[type=checkbox]",1)){this.onCheckboxClick(B,this.getNode(B))}else{if(B.getTarget(".x-tree-ec-icon",1)){this.onIconClick(B,this.getNode(B))}else{if(this.getNodeTarget(B)){this.onNodeClick(B,this.getNode(B))}}}},delegateDblClick:function(B,A){if(this.beforeEvent(B)&&this.getNodeTarget(B)){this.onNodeDblClick(B,this.getNode(B))}},delegateContextMenu:function(B,A){if(this.beforeEvent(B)&&this.getNodeTarget(B)){this.onNodeContextMenu(B,this.getNode(B))}},onNodeClick:function(B,A){A.ui.onClick(B)},onNodeOver:function(B,A){A.ui.onOver(B)},onNodeOut:function(B,A){A.ui.onOut(B)},onIconOver:function(B,A){A.ui.addClass("x-tree-ec-over")},onIconOut:function(B,A){A.ui.removeClass("x-tree-ec-over")},onIconClick:function(B,A){A.ui.ecClick(B)},onCheckboxClick:function(B,A){A.ui.onCheckChange(B)},onNodeDblClick:function(B,A){A.ui.onDblClick(B)},onNodeContextMenu:function(B,A){A.ui.onContextMenu(B)},beforeEvent:function(A){if(this.disabled){A.stopEvent();return false}return true},disable:function(){this.disabled=true},enable:function(){this.disabled=false}};