Marriage correction declined, despite his death

Hello there. I have a problem regarding fixing marriage details regarding the late voice actor Jan Rabson. Rabson was married to voice director Cindy Akers throughout most of his lifetime until his passing, so I was trying to include the date of his death being the last time Cindy was married to him. But just when I tried doing it, the site tells me that "it's not possible to correct directly". Not only for Rabson, but even when I tried doing it for Cindy to include an end date for Rabson due to his death, it has the same error. Can you fix this? Thanks.

(urn:alx:doc:937a93d2-a8ca-450d-ba84-56832d6ccf2d:2c986511-917e-40ac-b7d4-1bf8119534fc)