First of all, your router is configured to use WEP security, which only allows "5 or 13 ascii characters." That said, there are 2 versions of WEP, WEP 64-bit and WEP 128-bit. Wikipedia: "A 128-bit WEP key is almost always entered by users as a string of 26 hexadecimal (base 16) characters (0-9 and A-F)..." that means your password has to be EXACTLY 26 characters. If you want 10 letters/characters, you need to use either WPA/WPA2 as security. "10 to 26 hexadecimal characters" refers to the password requirements for WPA/WPA2 security.