It's a miracle...
As I mentioned above, the main settings of our workstations are controlled by policies at ESET PROTECT Server.
The setting of "License Interval Check" in the policy was Limited. Right now I set it to Automatic.
While doing that I had the only one workstation running at my company now and it had topic's warning message. The working day is over so all other workstations were switched off.
After changing the policy, the warning on the workstation disappeared by itself. There was no need to reboot workstation.
Then I woke up (via ESET PROTECT) another workstation. After it booted up there is no warning too.
So BradAtkins suggestion is true. And it proves that there is a bug in 9.0.2032.2.