Error message for "Invalid Username"

As per "UX guidelines" what should be the error message for a dimmpley Login for having 2 basic fields "Username" & Password.

So if a User Enter a username with "Space or special characters[,/<>{}]", should the message be very general saying "Invalid Username" or "Please enter a valid username"? or should it be more specific by telling them the special charaters they have added are not acceptable for this filed?

Here is what I am doing right now!

Please suggest!