Is there any error message, such as
/auser: insufficient parameters, after using the command?
Try using the 'guser' command instead of 'auser'
if ($1 == .adduser) {
guser user $2 3
notice $nick 11 $2 5 is now on the 4B5ot 4U5sers list4.
}
/auser relies on the address being in the IAL already
/guser forces mIRC to look the address up via /userhost.
And as sparta suggested, use code tags not quotes