i "guess" it may just some wrong code statement on your admin_review_avatar.asp. maybe missing a ' or &_ or Response.Write or something.. etc.
so if you got problem to judge what the right code statement, as Nikkol's suggestion, post a txt link to your file. then we will help you to correct this problem soon.
and what the addon modify to this file JUST add a small icon to indicate the different avatar group, that' all. so i think it's ok, if you just skip the modification to this file, it wo'nt affect anythng for this addon working.