Contradiction with Jonah 3:10
Jonah 3:10 describes God changing His mind about the destruction planned for Nineveh, which seems to contradict Isaiah 14:27's assertion about the unchangeable nature of God's plans.
Jonah 3:10: And God saw their works, that they turned from their evil way; and God repented of the evil, that he had said that he would do unto them; and he did [it] not.
Contradiction with Genesis 6:6
Genesis 6:6 speaks of God regretting that he had made humans on the earth, suggesting an ability for God to repent, which contrasts with Isaiah 14:27's emphasis on the firmness of His purpose.
Genesis 6:6: And it repented the LORD that he had made man on the earth, and it grieved him at his heart.
Contradiction with 1 Samuel 15:11
In 1 Samuel 15:11, God expresses regret for making Saul king, which contradicts the idea presented in Isaiah 14:27 of God's plans being irrevocable.
1 Samuel 15:11: It repenteth me that I have set up Saul [to be] king: for he is turned back from following me, and hath not performed my commandments. And it grieved Samuel; and he cried unto the LORD all night.