Ovirt engine cannot put host to maintenance mode with error: "Failed to change status of host due to a failure to stop the spm". Some investigation of log files gave understanding, that engine have trouble with some old tasks which remained unfinished.
Workaround in two steps:
- Remove old task from /path/to/storage/2c32c997-ef59-43de-bc9b-9f428722e0e9/master/tasks/*
- Restart engine.