Prompt computer name during OSD

I have a task sequence and I want it to prompt for computer name. I have a vbscript for this.

I created a package that holds a vbscript named PromptComputerName.vbs

Script looks like this:

strComputerName = InputBox("Enter computername") 
Set env = CreateObject("Microsoft.SMS.TSEnvironment") 
env("OSDComputerName") = strComputerName

Task sequence:

And the result

What is wrong with this one?