Stupid mistake:

 	var nicSyntaxButton = nicEditorAdvancedButton.extend({
              			width : '350px',
              		
              			addPane : function() {
              				this.addForm({
              					'' : {type : 'title', txt : 'Insert Code'},
              					'code' : {type : 'content', 'value' : '', style : {width: '340px', height : '200px'}}
              				});
              			},
              		
              			submit : function(e) {
              				var code = this.ne.selectedInstance.getContent() + "
"+this.inputs['code'].value.replace('	', ' ')+"
";
              				this.ne.selectedInstance.setContent(code);
              				this.removePane();
              			}
              		});