The record changed while you were editing it

An optimistic-concurrency refusal: the version you sent is not the current one, so someone else wrote to the record between your read and your write.

What to do

Re-read the record, re-apply your change to the fresh copy, and write again. Do not retry the same body with the old version — it will be refused identically, and if it were not, you would be silently discarding the other writer's change.