Author: Mariusz Litwińczuk. I contacted with TheBat! Support Team and now i know:
TheBat! can't be used as a fully usable client of Lotus Domino.
This program can't automatically switch to another instance of Lotus Domino server (due to failure).
When Lotus Domino switch to second instance, TheBat! will report error and can't download or send any mail.
In this case You must manually replace server address in program configuration to use second lotus domino mail instance.