What does Invalid Maximum Heap Size mean at Minecraft?

When I try to start Minecraft it crashes and the game output says:

Invalid maximum heap hize: -Xmx512M-XX: + UnlockExperimentalVMOptions

Process crashed with exit code 1

What can I do about it?

Have you ever played around with the parameters to assign Minecraft RAM?

If yes: undo.

If not, allocate more RAM to Minecraft.

How can I allocate more RAM to Minecraft?

Have a look here:

https://minecraftforum.de/topic/5570-bukkit-invalid-maximum-heap-size/

Simply reset the settings from the JVM. In 99% of the cases, that doesn't do anything.

Two questions:
Do you have java 64bit?

or an illegal character in your Minecraft name? (Process crashed with exit code 1) is an error message.