You're using a steering wheel motor or it's an integrated system? The message makes it sound like the steering wheel motor, but the replies make it sound like it's a hydraulic system?

If it's the steering wheel motor, and it does it when going over terraces....that's likely when that motor is needing to put out the most effort. If that's beyond what the max override is set to then it kicks out. You can change that on the steering settings. If it's doing this though even when you up that setting, the clutch may be starting to go out. It'll get worse and worse until it can't even engage on a line before giving that message.