Contradiction with John 16:13
This verse suggests that the Holy Spirit will guide believers into all truth, which could contradict 1 John 2:26 if interpreted to mean that external warnings or teachings are unnecessary.
John 16:13: Howbeit when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear, [that] shall he speak: and he will shew you things to come.
Contradiction with James 1:5
This verse implies that believers should ask God for wisdom when they lack it, suggesting a need for ongoing instruction contrary to the self-sufficiency implied in 1 John 2:26.
James 1:5: If any of you lack wisdom, let him ask of God, that giveth to all [men] liberally, and upbraideth not; and it shall be given him.