You are not able to Set as In Process a Visit with the status as Cancelled.
Reproducing the Issue
1. Go to Visits work center -> Visits view;
2. Open a cancelled Visit XXX;
3. Press Actions button;
4. "Set as In Process" option is greyed out.
This is expected system behavior. Currently the "Cancelled" status cannot be reverted in the Visit. Once this Visit is cancelled, a new Visit will have to be created for the account.
KBA , LOD-CRM , Cloud for Customer , How To