An error need you help 'object reference not set to an instance of an object'

Data source server changes，so i change the data source ,and refresh the query,it is ok and no any error.i didn't change any other setting.

But when i apply the changes in queries ,it going wrong and report an error'object reference not set to an instance of an object '.

whats wrong with it?and what can i do to find the reason for this error .

Kindly need you help ,thanks.