When I want to add an ItemAxe to my mod, it won't start the game. Is there some kind of bug with it?

Let me know.

When asking for help, always specify the Minecraft version you're using and post your code and the FML log/crash report.

 

In this case, the issue is almost certainly that you're using the vanilla

ItemAxe(ToolMaterial)

constructor and it's crashing with an

ArrayIndexOutOfBoundsException

. This is due to the constructor using the

ToolMaterial

's ordinal as an array index, so it only works with the vanilla

ToolMaterial

s. The solution is to use the

ItemAxe(ToolMaterial, float, float)

constructor added by Forge instead.

Yes Thanks that was exactly the problem