Contradiction with Exodus 20:4
This verse forbids making graven images, while 2 Chronicles 29:26 involves using instruments in worship, which could imply manmade tools in divine service.
Exodus 20:4: Thou shalt not make unto thee any graven image, or any likeness [of any thing] that [is] in heaven above, or that [is] in the earth beneath, or that [is] in the water under the earth:
Contradiction with Amos 5:23
Amos 5:23 dismisses musical worship altogether, contradicting the use of instruments in 2 Chronicles 29:26.
Amos 5:23: Take thou away from me the noise of thy songs; for I will not hear the melody of thy viols.
Contradiction with 1 Corinthians 14:34
This verse instructs women to keep silent in churches, which might conflict with organized musical worship involving all participants mentioned in 2 Chronicles 29:26.
1 Corinthians 14:34: Let your women keep silence in the churches: for it is not permitted unto them to speak; but [they are commanded] to be under obedience, as also saith the law.
Contradiction with Psalm 150:5
Psalm 150:5 encourages praising God with loud cymbals, which may seem in harmony rather than contradictory, but could conflict with the quieter worship styles some interpret from 2 Chronicles 29:26.
Psalm 150:5: Praise him upon the loud cymbals: praise him upon the high sounding cymbals.