Actually, Volvie, upon giving the matter some more thought, I think I can answer your question.
Can Chazal be wrong on matters of halacha? I think the question is meaningless simply because we have ruled, post facto, that the matters are as they say they are. Therefore, by definition, they aren’t “wrong.”
Example: We follow their opinion regarding tereifos, even though animals that they would have labeled tereifos can, in fact, live more than 12 months. Nonetheless, no one is (or should be) rushing to change the halachos of tereifos.
So, are Chazal infallible in halachic matters? No — we’ve simply decided to take their say-so on the matter.
The Wolf