Cost center &1/&2 locked for primary postings at this time

What causes this issue?

Cost center &V2&, controlling area &V1& is locked on &V3& for primary
postings.

System Response

At the very latest during posting for actual cost updates in CO (for
customer orders and external orders, this would be receipt of goods or
invoices; for settlement rules, this would be the settlement), the cost
center should no longer be locked. For this reason, a message is sent
with a variable message type.

How to fix this error?

If the message is a warning, remove the cause for the message, at the
latest before the posting of actual cost updating.
If the message is an error:
Remove the lock for primary postings in the master data record
Assign another cost center account
Assign another CO account assignment object
This message is sent as a warning in the standard system. You can make
the message an error message by changing the message type in
Customizing. Use the Implementation Guide under "Controlling: General"
and choose <DS:SIMG.SIMG_CFMENUORK3OBA5>Change message control</>. Enter
area KI and message number 170.

Error message extract from SAP system. Copyright SAP SE.