Brand new install on a Win7 laptop here; I had some underscores in my user name and alt. user name initially, and my IdentD User ID; I changed the first two as I was getting an error message, "*** Your username is invalid. Please make sure that your username contains only alphanumeric characters." - Even after that time, though, I kept getting that same error.
Turns out that the IdentD User ID - if it has an underscore or etc. in it - Triggers that same message, which is less than clear; Mentioning it as someone else could get caught and confused by this.
So, suggestion: Have the error report "*** Your " then one of username or alt username or identd user id then " is invalid. Please make sure that your username contains only alphanumeric characters."