Although cmclean.sql is no longer supported, but I had to search for it in the internet. I found it, then I ran it.
The problem then was solved.
Do you have an enabled button labeled "Fixed" in the Administer Concurrent Managers form?
If yes then click it for each manager and activate the manager.
I have solved the problem by running cmclean.sql. but for learning purpose, where is fixed button located?
I went to system administrator --> concurrent --> manager -->administer
and that button wasn't found.