Contradiction with Matthew 5:34
Zechariah 3:6 describes the angel admonishing Joshua with an oath, whereas Matthew 5:34 advises not to swear at all.
Matthew 5:34: But I say unto you, Swear not at all; neither by heaven; for it is God's throne:
Contradiction with James 5:12
Zechariah 3:6 presents an instance of an oath being used, while James 5:12 instructs to avoid oaths entirely, letting "yes" be "yes" and "no" be "no."
James 5:12: But above all things, my brethren, swear not, neither by heaven, neither by the earth, neither by any other oath: but let your yea be yea; and [your] nay, nay; lest ye fall into condemnation.