So...I did it....
For all of you have the same problem with activating RenderNodes for the (Box)License
There is a pitfall I forgot: Corona sent two SerialNumbers, one for the Workstations and one for the Rendernodes.
1- Get the right SerialNumber
2- Get the Key in the request-3dsmax.txt-File in C:\users\YOURNAME\AppData\local\CoronaRenderer
3- Open
https://corona-renderer.com/customer-zone/4- Type the right SerialNumber and the Key in Fields and click "Activate" (in "Activate Box")
5- Copy the (long) Activation-key in a text-file called "CoronaActivation.txt" in the Path under 2
now it should works....