During a previous project we needed to do an upgrade to the infrastructure of a diverse system and were attempting to use Agile methodology to upgrade one piece at a time. Incompatibilities and changes to data handling led to several errors that required changes to the stable systems to make them compatible with the upgraded systems. I established a pain threshold where analyzing and fixing the errors was taking more time than it was worth and negotiated with the client to do a full stop on features across the system and perform the upgrade system wide.