What is alphanumeric format mean?

I have flight simulator x and to play multiplayer i need to create a account with gamespy and it says my account must be less than 16 characters in alphanumeric format can someone please help me??

alpha stands for the alphabet characters, a through z, numeric stands for the numbers 0 through 9. It simply means that you can use any of the letters and numbers , but no "special characters", like the underscore (_).

Your e-mail address can't end with .net, try a .com.

this is almost definitely the problem http://answers.yahoo.com/question/accuse_write?qid=20080121012909AAtRNQ3&kid=Db9zAWvYMURq_bZ.VFPf&s=comm&date=2008-03-18+19%3A22%3A06&.crumb=