The Bible continually calls Jesus the Son of Man in several passages:
Mat 8:20 And Jesus saith unto him, The foxes have holes, and the birds of the air [have] nests; but the Son of man hath not where to lay [his] head.
Mat 9:6 But that ye may know that the Son of man hath power on earth to forgive sins, (then saith he to the sick of the palsy,) Arise, take up thy bed, and go unto thine house
Mat 12:8 For the Son of man is Lord even of the sabbath day.
Luk 9:44 Let these sayings sink down into your ears: for the Son of man shall be delivered into the hands of men.
Luk 9:22 Saying, The Son of man must suffer many things, and be rejected of the elders and chief priests and scribes, and be slain, and be raised the third day.
Jhn 5:27 And hath given him authority to execute judgment also, because he is the Son of man.
Jhn 6:27 Labour not for the meat which perisheth, but for that meat which endureth unto everlasting life, which the Son of man shall give unto you: for him hath God the Father sealed.
Jhn 6:53 Then Jesus said unto them, Verily, verily, I say unto you, Except ye eat the flesh of the Son of man, and drink his blood, ye have no life in you.
Jhn 8:28 Then said Jesus unto them, When ye have lifted up the Son of man, then shall ye know that I am [he], and [that] I do nothing of myself; but as my Father hath taught me, I speak these things.
So it's pretty clear that Jesus is the son of man according to the Bible. Now since we know that, let us read what the OT says concerning the son of man.
1 Praise ye the LORD. Praise the LORD, O my soul. 2 While I live will I praise the LORD: I will sing praises unto my God while I have any being. 3 Put not your trust in princes, nor in the son of man, in whom there is no help. 4 His breath goeth forth, he returneth to his earth; in that very day his thoughts perish. 5 Happy is he that hath the God of Jacob for his help, whose hope is in the LORD his God: 6 Which made heaven, and earth, the sea, and all that therein is: which keepeth truth for ever: 7 Which executeth judgment for the oppressed: which giveth food to the hungry. The LORD looseth the prisoners: 8 The LORD openeth the eyes of the blind: the LORD raiseth them that are bowed down: the LORD loveth the righteous: 9 The LORD preserveth the strangers; he relieveth the fatherless and widow: but the way of the wicked he turneth upside down. 10 The LORD shall reign for ever, even thy God, O Zion, unto all generations. Praise ye the LORD
So note, the OT claims that you should not place your trust in the son of man because there is no help! One thing to make clear is the verse does not mean the son of men are liars, all the verse means is that you should not trust the son of men as you do with God. So hence if the Bible is telling us that we should not place our trust in the son of men as we do with God then this means Jesus is not God because he was a son of man!
So how can Jesus be God when we are told to not place our trust in the son of man? How can Jesus be God when we are told there is no help in the son of man? The answer to these questions are simple, Jesus is not God!
So to summarize we find out that:
1-Jesus is the son of man
2-The Bible states that you should not trust the son of man
3-The Bible states that there is no help in the son of man
4-Jesus is the son of man so therefore we can't trust him
5-Jesus is the son of man therefore there is no help in him
6-We must place our trust in God in whom there is help
7-Jesus is not God
So very simple isn't it?
Again the verse does not mean that the son of men are liars which is why you don't trust them, all it means is that you should not place your trust in the son of man as you do with God.
Now just incase a Christian wants to say that this is the OT so it does not apply, here is a verse which refutes this claim:
2 Timothy :
All scripture [is] given by inspiration of God, and [is] profitable for doctrine, for reproof, for correction, for instruction in righteousness:
So all scripture is God breathed including the OT. All scripture is there for doctrine, reproof, correction and instruction. So it is clear that the Psalm verse falls under the category of instruction by telling us to place our trust in God and not the son of man. It also falls under the category of doctrine since it makes it clear that you should place your trust in God and he is the only one who can really help you.
So the Christians have no way out of this. Jesus is not God!