The City of Birmingham can be added to the long list of organizations that went bankrupt trying to replace their ERP system. They were running a heavily customized SAP system and tried to implement Oracle Fusion. As often happens in this kind of project, the costs exploded from the initial estimate of $25 million to $125 million by the last count. They are not done yet, and since they’ve stopped paying their bills, they might never be.
When you are faced with a legacy system no longer fit for purpose, don’t fall prey to the dangerous illusion that you can run one large project to replace it. A project is a collaborative enterprise intended to reach a well-defined goal. But for a large IT project, the project duration alone (four years and counting in Birmingham) ensures that the goalposts will have moved several times before you are done. Your Program Manager is not likely to be among the few hundred people in the world with the exceptional project and change management skills needed to pull off such a project.
A series of smaller projects to carve out and replace functionality in smaller chunks does not promise to solve all your problems in one fell swoop. But it has a much higher chance of success.