In addition to business retraining in new processes, the users of the new system will need training in its use. Production of a user manual is only a small part of the training package; there will need to be a training session for the trainers and scheduled training sessions for users (and an associated lost opportunity cost as these users take time out from their day job). Finally, a dedicated training environment and database may have to be provided.
The timing of training is critically important, too. If it's too far ahead of the rollout of the system, the users will forget what they learned. If it's after the rollout, there may be irreparable damage done to the perception of the system during the "suck it and see" untrained period of use.