I figured it out by myself.
If you want to use a CustomEvent(replicated by server) you have to make sure that the Blueprint is only spawned on the server and then replicated. So you have to use an “AuthoritySwitch” and plug the Blueprint to “Authority”.
If you don’t explicity spawn (in my case) “ConstructionManager” on server with the “AuthoritySwitch” it will be spawned on the client and the server. The server then replicates it to client which means you do have to copys of “ConstructionManager” on the client then. The problem is that the original version of the “ConstructionManager” on the Client gets priority and does not have a verison on the server. So it is not able to Call a Function on the Server.
To put in in a nutshell:
If you want a Blueprint to be able to perform “CustomEvents” with “Replicate on Server” you have to make sure that it is only spawned on server. Do this with an “AuthoritySwitch” before Spawning it. Then make sure to set “Replicates” in the Blueprint settings.
For more details see:
http://cedric.bnslv.de/Downloads/UE4_Network_Compendium_by_Cedric_eXi_Neukirchen.pdf