Well did your adoptable site already have members before you installed forum? If so, you have to tweak your forum database a lot to make it work. Also the forum integration script was for MyBB 1.6, so if you have MyBB 1.8 you need to change something. Look at this post from Kyttias to fix your problem:
http://mysidiaadoptables.com/forum/p...php?issueid=52