What I have?

I have normal web application and it has 3 site collections with name, "PDirectory". Other than this I have only Central administration web application in the farm.

What I want?

I want to delete that web application, "PDirectory".

What problem am I facing?

I am not able to delete the web application. I get below error when I try to delete it but, the site collections got deleted!

Error:

An object in the SharePoint administrative framework, "SPWebApplication Name=XXX Parent=SPWebService", could not be deleted because other objects depend on it. Update all of these dependants to point to null or different objects and retry this operation. The dependant objects are as follows: SPFarm Name=SharePoint_Config SPFarm Name=SharePoint_Config

at Microsoft.SharePoint.Administration.SPConfigurationDatabase.DeleteObject(Guid id) 
       at Microsoft.SharePoint.Administration.SPConfigurationDatabase.DeleteObject(SPPersistedObject obj) 
       at Microsoft.SharePoint.Administration.SPPersistedObject.Delete() 
       at Microsoft.SharePoint.Administration.SPWebApplication.Delete() 
       at Microsoft.SharePoint.ApplicationPages.DeleteWebApplicationPage.BtnSubmit_Click(Object sender, EventArgs e) 
       at System.Web.UI.WebControls.Button.OnClick(EventArgs e) 
       at System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) 
       at System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) 
       at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) 
       at System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) 
       at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

Can somebody tell me how I can delete this web application?

Thanks in advance!