The Bible says that a prophet who predicts something that does not occur is speaking words that the Lord did not speak, but that is exactly what Jesus did, if you can believe the author of Mark. Here are the relevant verses:
"When a prophet speaks in the name of the Lord, if the word does not come about or come true, that is a word which the Lord did not speak;" (Deuteronomy 18:22).
Jesus said, "These signs will accompany those who believe...if they drink any deadly thing, it will not harm them" (Mark 16:17-18)
However, it is NOT true that those who believe in Jesus can drink poison without harm, so if Mark is correct and Jesus really said this, Jesus made a prediction that doesn't come true, so this prediction wasn't from the Lord. But, this contradicts 2 Timothy, which says that "all scripture is God-breathed."
On other hand, if Jesus didn't really say this, then Mark was wrong and the Bible is in error. Thus, either way, the Bible is in error.
Joseph F. Alward
"Skeptical Views of Christianity and the Bible"
http://members.aol.com/jalw/joseph_alward.html