look

$iif(condition,$true,$false)

so when u put $iif($group(#away).status iswm on,$me $+ 's Away System,)

if ($group(#away).status iswm on) $me $+ 's Away System
else $me $+ 's Away System

then whatever the condition is return "$me $+ 's Away System"

now u put $group(#away) where is the group?

take look at /help $group

u have an indeclared alias "away"

so your code must be like this

menu channel {
  .$iif(%me_away,$me $+ 's Away System,$me $+ 's Present)
  ..Away:/set %reason $$?="Why be youz away?" | /set %anick $$?="What would u like ur away nick to be?" | /set %eatime $$?="How long will you be away (Estimate)?" | /ame 12,1is away, Reason: 4,1( $+ %reason $+ ) 6,1I will be away for an estimated time of:9,1 %eatime | set %away.time $ctime | set %me_away 1 | nick %anick
  ...Back:/set %bnick $$?="What would you like ur Back Nick to be?" | /ame 12,1is back from: 4,1( $+ %reason $+ ) 6,1I was away for $duration($calc($ctime - %away.time)) | unset %reason %me_away | nick %bnick
}