You're going to want to post at least the line of code that refers to. Go to your Login.dm file, hit control-G and type in line 73 as the line you want to go to. Copy and paste that section of code here so we can offer you a bit more help. "Cannot modify null.[whatever]" is usually a problem when you're trying to refer to a variable for something that doesn't exist, or doesn't exist yet. I am assuming you're trying to set the name for a mob that's being logged in, but you're not referring to it correctly.