Status transitions within CWC can be customized so that it is only possible for certain statuses to transition into others. For example, in the image below if the current status is the FromStatus column then the only possible statuses that it can transition to are checked on that row. This means that for a status of In Progress, the only possible status to transition to is Complete.

These settings can be modified or removed by clicking the green pencil icon to the left of each row.