In order for a user to be able to change a job's workflow status from To Mask to To Validate, the job must have 0 images left To View, 0 images left To Edit, and all the Active Users must confirm they will not return to the job (their name will be green). Once those three conditions are met, a To Validate button will appear in the Change Status column of the Jobs page.
As shown in the image below, the job with 0 images To View, 0 images To Edit and the active user (in this case Karen Comeau) has confirmed she will not return to the job (this is why the user's name appears green - otherwise it would appear red), so we can now click on the To Validate button.
This is also visible within the KO Viewer and KO Editor. Both undefined and selected (for all active users) must be zero and all active users must confirm they will not return to the job.
If a user's name remains red, the KO Administrator will not be able to move the job along in the workflow. Please see the section titled Force Work Complete of the Job Details Page for instructions on how to force a user's work complete.