NullReferenceException while running SharePoint products ( Central admin site is not working)

Question

We are able to access the sharepoint sites but the centeral admin is not working so tried to run the share point product with exsisting farm and sharepoint_configdb. After step7, we are getting error as NullReferenceException and product wizard failed. Not able to run centeral admin.

Detailed Exception: 01/08/2013 16:07:36 19 ERR
Task applicationcontent has failed with an unknown exception 01/08/2013 16:07:36 19 ERR Exception: System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.SharePoint.Administration.SPWebApplication.CopyAppDomainDirectories(DirectoryInfo vrPath, OverwriteSetting overwrite) at Microsoft.SharePoint.Administration.SPWebService.ApplyApplicationContentToLocalServer() at Microsoft.SharePoint.PostSetupConfiguration.ApplicationContentTask.Run() at

Microsoft.SharePoint.PostSetupConfiguration.TaskThread.ExecuteTask()

please help us.