You may use PerX injector, It is eaiser.
Also, Jabberw0ock just posted a Solution for that Process ID error. And i quote.
Couldn't get process ID. = It means Game Guard is protecting the AVA.exe process and hiding it. In this situation you didn't bypass Game Guard so you have to do it first. In task manager the process isn't shown, that's the problem.
Couldn't open process with access to it. = This time the problem is the same(Game Guard is protecting the process) but you can overcome this by injecting while the process is in the loading stage.