Search:

Because you are trying to do an update query on a connection with an open datareader.
You also should not be creating a new instance of the cmd object within your loop.

Not sure why you are even...

Dim RefID As New System.Data.SqlClient.SqlCommand(("Select RefNo From dbo.QryRefNo WHERE ChangeRaisedDate = @ChangeRaisedDate"), nextconn)
cmd.Parameters.AddWithValue("@ChangeRaisedDate",...