I'm guessing that it's because you are over the character limit. If player names are shorter than you won't have the problem. Or, to make it safe for both short and long names you will need to truncate all the names to a fixed length.
Or, I think, because it is not the new style menu you can just make the array szMenu[] declared on line 101 longer (the 256 to something bigger). That is if there is not a limit set by the HL engine for displaying menus.