"Then Jesus said unto them, Take heed and beware of the leaven of the Pharisees and of the Sadducees.
7And they reasoned among themselves, saying, It is because we have taken no bread.
8Which when Jesus perceived, he said unto them, O ye of little faith, why reason ye among yourselves, because ye have brought no bread?
9Do ye not yet understand, neither remember the five loaves of the five thousand, and how many baskets ye took up?
10Neither the seven loaves of the four thousand, and how many baskets ye took up?
11How is it that ye do not understand that I spake it not to you concerning bread, that ye should beware of the leaven of the Pharisees and of the Sadducees?
12Then understood they how that he bade them not beware of the leaven of bread, but of the doctrine of the Pharisees and of the Sadducees." (Matthew 16:6-12, KJV.)
Some universalists have suggested that the doctrine Jesus was telling them to beware of was, in the case of the Sadducees, the belief that there was no resurrection, and in the case of the Pharisees, the belief of eternal torment. What I'm wondering is whether there is anything substantive to back this up. Are there any other beliefs that either group held that Jesus could have been referring to? I'll briefly state the reasons I can see to hold such a position, with the qualification that I do not know a lot about either group.
Doing a search for the Sadducees, they are only mentioned rarely. Aside from several references where they are grouped together with the Pharisees (e.g. Matthew 3:7, and the text in question) and a couple references in Acts, there is one recorded confrontation between Jesus and the Sadducees, found in all three synoptic gospels; the Sadducees concoct a scenario involving Levirate marriage in order to try to disprove the resurrection, but Jesus refutes their beliefs. (Matt. 22:23-33; Mark 12:18-27; Luke 20:27-40.) In addition, in Acts 23:6-8, Paul offends the Sadducees by stating that he believes in the resurrection of the dead. Finally, there is Paul's passionate argument in 1 Corinthians 15 for the resurrection of the dead. Now, given all this, I think it's safe to say that the resurrection from the dead was probably what Jesus had in mind when He was referring to the Sadducees; I do not know if they had other objectionable teachings, but if they did, they are never mentioned as anything Jesus or the early church fought against.
Now, the question is what the Pharisees were teaching that was so objectionable. Given that Jesus grouped their errors together with those of the Sadducees, it is somewhat attractive to think that they may have erred on the same subject; but this is not necessarily the case, and we do not find Jesus or Paul explicitly arguing against eternal punishment in the same polemical way they defended the resurrection of the dead. Indeed, Jesus would not have seemed like a universalist to His audience (Gregory MacDonald, for instance, concedes this point), and some of his parables have been quoted strongly to prove the doctrine of endless punishment. It is, perhaps, significant that He uses more ambiguous terminology than His contemporaries (avoiding the use of aidios, primarily), but He does not usually offer hope of redemption from the punishment; and if at other times He hints at universalism, they are only hints at best.
However, are there any other good candidates for the teachings of the Pharisees that are to be avoided? The first one that comes to mind is the oral law, but I'm not sure whether Jesus would have particularly objected to that or not. OTC claims that it was because the Pharisees and the Sadducees believed in free will, but that's OTC for you.