Command doesn't work - failed to call hook

Hi!
I'm writing a plugin, which derives from CovalencePlugin. I'm trying to add a command, which could be called from the chat/console:

Code:

[Command("MyCommand")]
void commandHandler(IPlayer player, string command, string[] args)
{...}

Everything seems to be ok, but calling the command from the game (Hurtworld) causes an error:

Code:

Failed to call hook 'commandHandler' on plugin 'MyPlugin v0.1.0' (InvalidOperationException: Operation is not valid due to the current state of the object)

Could anyone help me?