You need to have the proper ODBC connection configured. If your app is referencing an ODBC that doesn't exist or the server location or name has changed, then it won't find your new server. Did you change the name of the server from an old server name?
Also, your app may not have the proper credentials. It may have credentials from the old server, or you may not have supplied them to your code, or you may not have granted sufficient rights on the new server.