Question:
What teaching should exclude someone from fellowship?

Answer:

Be careful of doctrines that affect the work or person of Jesus (denying the eternal Sonship of Christ, saying that Jesus’ work on the cross wasn’t enough to pay for sin, denying His crucifixion or resurrection, etc.).  “Whosoever transgresseth, and abideth not in the doctrine of Christ, hath not God” (2 John 1:9). We should also be careful of any teachings that aren’t supported by Scripture.  People in the assembly do disagree on some issues, such as predestination, but it’s not reason to divide.