SPWebConfigModification not working

Hi,

I'm trying to add entry in web.config using below code

public override void FeatureActivated(SPFeatureReceiverProperties properties)
        {
           
            SPWebService newService = SPWebService.ContentService;
            SPWebConfigModification customModification = new SPWebConfigModification();
            customModification.Path = "configuration/system.web";
            customModification.Name = "browserCaps";
            customModification.Sequence = 0;
            customModification.Owner = "UserName";
            customModification.Type = SPWebConfigModification.SPWebConfigModificationType.EnsureChildNode;
            customModification.Value = "<browserCaps></browserCaps>";
            newService.WebConfigModifications.Add(customModification);
            newService.Update();
            newService.ApplyWebConfigModifications();

            SPWebConfigModification customModification1 = new SPWebConfigModification();
            customModification1.Path = "configuration/system.web/browserCaps";
            customModification1.Name = "result";
            customModification1.Sequence = 0;
            customModification1.Owner = "UserName";
            customModification1.Type = SPWebConfigModification.SPWebConfigModificationType.EnsureChildNode;
            customModification1.Value = "<result type='System.Web.Mobile.MobileCapabilities, System.Web.Mobile, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'/><filter>isMobileDevice=false</filter>";
            newService.WebConfigModifications.Add(customModification1);
            newService.Update();
            newService.ApplyWebConfigModifications();

        }

I'm getting "Error occurred in deployment step 'Activate Features': '' is an invalid expression."

I'm I doing anything wrong here? please help.