HI At principal Solution field not need in Form before Status be eq. Completed. 4 solutions: 1.If you use 4.5 and SP18 you can use Dynamic form for this task. 2. Possible create UI Rule, before save if this field not empty and status!=Completed Error messages. 3. DB Rule Clear Solution if Status ... 4. Use more 2 Roles where Status Waiting excluded, use Status Access in role, in first Role set "Status to" = one status before Waiting, in second role set "status from" = one status after Waiting.