I tried to sign up with the name "Sans Halo" but the game said it was unacceptable because it didn't sound like a name. I guess Han Solo would be unacceptable based on that criteria also. I don't really understand why it matters, why that particular name was rejected, or exactly what criteria is used to determine whether a name is acceptable or not.
It doesn't sound like a name to me either. There are no exact criteria besides what whoever is accepting the name feels sounds like a "name". And Sans Halo is just Han Solo mixed up and doesn't really sound like a name. You should just try a different name, Ideally not based off a Star Wars Char. name. You might go look at some random name generators to get ideas and such before deciding on a 'unique' name. Your going to have to live with this name for quite a long time, so be sure you like it.