Server keeps shutting down: "too many virtualservers running, shutting down!"

I had to go to the 32 bit version with 3.12. now after starting the server he shuts down after a few minutes.
In the Logfiles I found: “too many virtualservers running, shutting down!”

But I use only one server and don’t have virtual instances.

What can I do?

Maybe too many Slots?
EDIT: Try it with less than 32 Slots

Not the slot settings is the problem.
Self hosted server or provided by a hosting ?

Guess issue is solved already.

Same old story as usual:
User did not stop his old server or killed the process to stop it (did not follow any guide how to stop the server) before updating the server.