[Fixed]
The problem for me was that I needed to have the path to the java.exe, instead of just 'java' in my launching bat file. This for some reason was already done for the normal server, and I did not notice it.
I am new to the whole world of servers and stuff, especially with forge. I noticed, for the normal minecraft server, that it is much better to have the server running without a gui. I am wondering, how should I do this? Is it even possible? I have tried the normal thing users would be able to do with a vanilla minecraft server: "java -Xms4G -Xmx4G -jar minecraft_server.jar nogui". I have 64bit Windows 10, 64bit java, if that is required. Any help would be welcome!