Ich möchte mein Forge Server starten doch bekomme ich jedes mal eine Fehlermeldung 

C:\Users\fabri\Desktop\Thaumcaft Server>java -Xmx10G -Xms10G -jar server.jar nogui
A problem occurred running the Server launcher.java.lang.reflect.InvocationTargetException
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:568)
        at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.run(ServerLaunchWrapper.java:70)
        at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.main(ServerLaunchWrapper.java:34)
Caused by: java.lang.ClassCastException: class jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to class java.net.URLClassLoader (jdk.internal.loader.ClassLoaders$AppClassLoader and java.net.URLClassLoader are in module java.base of loader 'bootstrap')
        at net.minecraft.launchwrapper.Launch.<init>(Launch.java:34)
        at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
        ... 6 more

C:\Users\fabri\Desktop\Thaumcaft Server>pause
Drücken Sie eine beliebige Taste . . .
 

was soll ich tun

Make sure you are using Java 8 - currently you are using a newer version

Here's a quick fix: try switching back to Java 8 for your server. You can download it from the official Oracle website or use OpenJDK versions if you prefer. Once you've got Java 8 installed, make sure to point your server startup script to use this specific Java version. This change might just solve your launch problem and get your server up and running smoothly.