Hi all. If you have problem with alerts after migrate SharePoint, you must open SQl content database and you must open  SchedSubscriptions  table. In this table you look all user alerts. But if you look SiteUrl column, you saw url old sharepoint server.

You must run this SQL script

UPDATE [dbo].[SchedSubscriptions]
SET [SiteUrl] = ‘New URL’

GO

String script = String.Format("window.frameElement.navigateParent(‘{0}’);",  

SPHttpUtility.EcmaScriptStringLiteralEncode(web.Url + "/" + newView.Url));

            Page.ClientScript.RegisterStartupScript(Page.GetType(), "redirectToPage", script, true);