Depreciation key & cannot be changed. (& depreciation posted)

What causes this issue?

You want to change the depreciation key.

System Response

You cannot change a depreciation key in an area in which the
depreciation key has already been used for the automatic entry of
accumulated depreciation, when depreciation has already been posted.

How to fix this error?

First you have to correct the depreciation already posted using a
write-up. Then you can change the depreciaton key.

Error message extract from SAP system. Copyright SAP SE.