Integrations do not normally fail because of middleware technology
An integration between two systems, say system A and system B, might fail when one of the following things happen. It could break when System A was updated and some integration points do not send or receive the necessary information. It could break because System B was updated and some integration points do not send or receive the necessary information. The integration between two systems rarely break because the middleware technology handling the integration went through some change.
Lack of attention from project team is the main cause for failure
Integration also becomes an issue when project teams do not pay attention to it or do not keep time and money aside to address it. Unfortunately, software vendors sometimes mislead customers by saying either integration is not necessary or is so simple that they do not have to worry about it. In some cases vendors show a tool and say that the tool will solve all the integration problems. It is a bit like showing an oven to a group of aspiring chefs and saying that the oven is all they need to make great food.
I have been pointing this out to customers and have been urging them to pay more attention to integration content and the business value it brings for them. I have also been urging customers to keep time, money and more importantly mind share aside for the topic of integration for over a year now.
This has started paying off. Those customers who planned to address integration early in their projects completed their projects will a lot less stress compared to the ones that did not.