The problem for RBS - and frankly most of the other big banks - is that it has been under investing for years in the IT infrastructure. These are the back room computers that make all this work normally.
In fact, a lot of the systems date back to the 1980s or 1990s and one former RBS IT executive described to me a "culture of fear" within the teams there. They don't want to touch these systems because often when they do, they break.
RBS says it is tackling the IT problems, it's investing an extra £450m but with this latest collapse happening just as the Christmas spending really begins to gear up, they might be wishing they out that money in some time ago.