Item was not crawled because of a password change. Update password and retry crawling

Hi,

My Search service application was stopped crawling and I got error message "Item was not crawled because of a password change. Update password and retry crawling" from log. I have updated the default content access account and its corresponding application pool account. But still I am getting the same error. So that I have created new search service application and crawled the data successfully. But when I switched to new service application( set as default search service application) I got error in the search. But search is working in the old search service application ( but crawl is not working).

I got search error from the log mentioned below

CoreResultsWebPart::OnInit: Exception initializing: System.NullReferenceException: Object reference not set to an instance of an object.   
 at Microsoft.Office.Server.Search.WebControls.CoreResultsWebPart.SetPropertiesOnQueryReader()   
 at Microsoft.Office.Server.Search.WebControls.CoreResultsWebPart.OnInit(EventArgs e)

Internal server error exception: System.NullReferenceException: Object reference not set to an instance of an object.   
 at Microsoft.Office.Server.Search.WebControls.CoreResultsWebPart.SetPropertiesOnQueryReader()   
 at Microsoft.Office.Server.Search.WebControls.CoreResultsWebPart.OnInit(EventArgs e) System.NullReferenceException: Object reference not set to an instance of an object.   
 at Microsoft.Office.Server.Search.WebControls.CoreResultsWebPart.SetPropertiesOnQueryReader()   
 at Microsoft.Office.Server.Search.WebControls.CoreResultsWebPart.OnInit(EventArgs e)

Thanks in advance.