If the approval page fields include any custom fields on standard objects, you need to manually add those custom fields to outbound change sets. The View/Add Dependencies option for selecting change set components won’t include these fields.
If the approval process references any post templates that contain custom fields, then you need to resave those post templates in the originating organization before adding them to the change set. From Setup, click Create | Workflow & Approvals | Post Templates. For each post template, click Edit and then Save.
Change sets don’t include the order of active approval processes from the source organization. You may need to reorder the approval processes in the destination organization after deployment.
If you change the Unique Name of an approval process that was previously included in a change set and deployed in another organization, and you resend the approval process via a change set, a new approval process will be created upon deployment in the other organization. The previously deployed approval process will not be modified.