PO Approver setup change with signature file

hi, the backup PO Approver left the company and i need to replace that person with another person from the company, The approver also has their own signature file. When i change the previous person to the new person with their signature file, during po approval process, the users are getting the message: "PO Approver signature setup are incomplete. PO Acknowledgement emailing aborted.

How do i fix this issue? I placed the new signature file in $OA_MEDIA directory - same place as previous persons signature file.

Any help is appreciated. This is E-business suite 12.1.3

Thanks.